Hillary Rodham Clinton finally announced her opposition to the Keystone XL pipeline project that has become a lightning rod in the energy debate after months of demurring. But Clinton said Tuesday that she had been hinting about her position for weeks, talking to labor leaders and others, before she finally was asked the question at a forum in Iowa.

Speaking later with the Des Moines Register's editorial board, Clinton said she'd been reluctant to weigh in on the issue soon after she left the State Department, saying it was important to give President Obama and Secretary of State John F. Kerry "the space and time to make that decision."

"But it has now been a long time since I left the State Department," she said, adding that she telegraphed in recent weeks she would soon make her view known publicly. "I had no idea that I would be asked today, but I had put people on I think adequate notice that I was going to respond when I was asked."

Donald Trump is fighting back against an influential conservative group's ads that have been running in Iowa since last week.

A cease-and-desist order sent on Tuesday by Trump's attorney, Alan Garten, to officials at the Club for Growth details what he says are defamatory "attack ads" that falsely claim Trump supports the "highest tax increase in history."

In a 30-second spot from the group, which looks to portray Trump as more in step with Democrats than Republicans, he's slammed for wanting to impose a “14.25% net worth tax on the super rich” to pay the national debt.

The $1-million ad buy by the group began last week and is set to run through next week.

"I am not surprised the dishonest, irrelevant and totally failing Club for Growth has resorted to attacking the definitive front-runner, especially after I refused to contribute to their pathetic group," Trump, who plans to release a detailed tax policy plan in the coming weeks, said in a statement.

He notes that the ad assails him for a concept he suggested more than a decade ago and has not supported since, which he says makes it libelous.

In a response, David McIntosh, president of the Club for Growth, said the billionaire businessman's comments make it clear the ads are right. McIntosh's group is widely viewed as a preeminent institution promoting Republican adherence to free-market and free-trade agendas.

"Trump's own statements prove that our ads are accurate. They will continue to run. We suggest that Donald grow up, stop whining and try to defend his liberal record," McIntosh said.

Recent polls since last week's debate show Trump still polling strong in Iowa, which will hold the first nominating contest in early February.

Hillary Rodham Clinton wouldn't take sides earlier this summer over the proposed Keystone XL pipeline, which would carry oil from Canada to refineries on the Gulf Coast. Because it would cross the border, it requires a permit from the State Department, which continues to review the project.

Former Arkansas Gov. Mike Huckabee, continuing an effort to cater to the powerful social conservative bloc in the Republican base, unleashed a blistering attack on President Obama on Tuesday for planning, in his words, to turn Pope Francis' visit to the White House "into a politicized cattle call for gay and pro-abortion activists."

In a series of tweets and an op-ed for the conservative Daily Caller , Huckabee lamented that whereas the Obama administration showed respect to the corpse of Osama bin Laden under Muslim tradition and Obama has bowed to a Saudi king and the Japanese emperor, the president "scorns millions of believers in Christ at home" by including abortion and gay rights activists at a White House arrival ceremony planned Wednesday.

"Exploiting the pope for cheap political points at the expense of millions of Americans and Catholics around the world is a shameless new low for this administration," Huckabee said.

Such loaded rhetoric is not new for Huckabee, who was himself harshly criticized this summer for comparing Obama's quest for a nuclear accord with Iran to marching Israelis to "the door of the oven."

White House officials declined to react to Huckabee's specific criticisms Tuesday. They've noted that with 15,000 people expected on the South Lawn for the pope's arrival, it is natural to expect a "diverse crowd." A Vatican spokesman denied any tension over the guest list, saying it "never comments on those invited by a head of state to be present for a welcoming ceremony of the pope."

And while Huckabee accuses Obama of a lack of respect for Pope Francis, the White House is in fact going out of its way to make his visit a showcase event, in part because of their shared commitment to issues like climate change and human rights.

"When the president sits down with Pope Francis tomorrow in the Oval Office, the president will not arrive at that meeting with a political agenda," Press Secretary Josh Earnest told reporters. "This is an opportunity for two men who have so many values in common, to talk about the efforts that they are taking in their respective and quite different roles to advance those shared values."

Another Republican presidential hopeful, Carly Fiorina, told NBC's Jimmy Fallon that she looked forward to the pope's visit and offered more temperate criticism of Democrats.

"I don't agree with him on all of his politics for sure," she said. "I do think it's interesting that you know Democrats say, 'Oh, he's so right about the environment and he's so right about capitalism,' but they don't really talk about his belief in the sanctity of life because that they don't agree with," she said on "The Tonight Show."

Former Florida Gov. Jeb Bush will be attending the papal mass in Washington on Wednesday. In an op-ed on CNN.com, Bush wrote about his conversion to Catholicism and praised Francis' visit as a reminder that "we can protect religious freedom and the right of conscience while respecting those with opposing views."

As Hillary Rodham Clinton put her campaign spotlight Monday on the South -- leaning into Obamacare and picking a fight with a GOP governor -- some high stakes behind-the-scenes work was going on in California.

That's where Clinton campaign manager Robby Mook had traveled. He planned visits in the Bay Area to reassure, reenergize and recommit some key players in the Clinton West Coast money machine.

If there is one place in the country the campaign cannot afford to be overtaken by the donor gossip mill, it is California. It accounts for so much of Clinton's campaign cash that any time its big donors grow anxious or hesitant, it's a potential crisis for the campaign. It is why the Clinton team is around the state so much.

Mook's stops, according to donors who were invited to join the conversation, included the homes of Susie Tompkins Buell and Amy Rao. Buell, who lives in San Francisco, is one of Hillary Clinton's close friends. She is the founder of Esprit clothing. Rao is a Silicon Valley businesswoman and prodigious fundraiser.

The visits were not particularly remarkable. They have long been part of the Clinton playbook. Campaign chairman John Podesta -- who, like Mook, wields huge influence over the Clinton operation but tends to keep to himself when reporters come calling -- has also been hitting the road.

It is all part of the care and feeding of major donors, or "whales" in the language of fundraising. These people tend to have strong, often conflicting opinions about how the campaign is navigating every bump in the road -- whether it is the festering email server controversy or Clinton's plunge in the polls in New Hampshire. Mook's challenge is to make them feel like their opinions matter to the campaign, while also persuading them that the political professionals back at campaign headquarters in Brooklyn have it all under control.

Clinton herself will be back Sunday, Monday and Tuesday for a series of fundraisers in Los Angeles and the Bay Area.

After he was excoriated for the assertion, the candidate tried to clarify his comments over the weekend that no Muslim should be president.

Riding high after a strong performance in last week's Republican presidential debate in Simi Valley, Fiorina visited the “Tonight Show” on Monday and tried to show voters her lighter side.

With an assist from the show's host, Jimmy Fallon, Fiorina sang a lullaby she sings to her dog, Snickers.

"My name is Snick and I'm lazy, please don't take a walk with me. I'd rather stay right here at home instead, I want to lay back down in my nice warm bed. My name is Snick and you're going to have to carry me," sang Fiorina to applause from the audience.

In recent weeks, Fiorina, the former Hewlett-Packard CEO, has surged in the polls but still trails front-runner Donald Trump. On the show Monday, she also doubled down on her opposition to any dialogue between the United States and Russia were she to become the next commander in chief.

Since Fiorina entered the race, she has insisted the U.S. needs to reassert itself as a global heavyweight. Fiorina, who once met Russian President Vladimir Putin at a major economic conference in Asia, stressed that as president she would not meet with him again.

“He lusts for power and he's gathered up a lot of it," Fiorina said on the "Tonight Show." "He's a very bad actor and it's a very bad thing that his fighter jets and his soldiers are sitting in Syria right now. That's a bad thing."

Russia is an ally of the government of Syrian President Bashar Assad, who has held on to power during his country's civil war, now dragging into its fourth year, having forced millions to flee the country.

"Putin needs to see he faces strength and resolve and leadership from the United States," Fiorina said.

But some Republican challengers have called Fiorina's view toward Putin shortsighted and irresponsible. The U.S. and Russia began military-level talks last week over the conflict in Syria, a victory for Putin as he tries to break out of the isolation other countries have imposed on Russia because of its support for separatists in Ukraine.

Although Scott Walker said he was bowing out of the presidential race to help the Republican Party rally around an alternative to “the current front-runner” -- whom he declined to name -- Walker's problem wasn't so much Donald Trump as himself.

The Wisconsin governor, a novice to national politics, was plagued by blunders even before declaring his candidacy. In February, for instance, he said his struggles with state employee unions had prepared him to take on Islamic State.

When he entered the race in July, however, he was polling strong in Iowa, which holds the first nominating contest. His Midwestern roots and his family's religious ties made him a favorite.

By Sunday, after a lackluster performance in two debates, his support had plummeted to zero in a CNN/ORC poll. His fundraising had tanked too.

Here are three areas where Walker stumbled.

His entrance into the race

Walker entered the 2016 campaign under a spotlight no candidate would enjoy -- a public tiff with his family.

When the U.S. Supreme Court ruled in June that same-sex couples had a constitutional right to marry, Walker objected.

“I believe this Supreme Court decision is a grave mistake,” he said.

The next day, Walker toned down his comments, noting that the high court's ruling was the law of the land.

But the damage was done, casting Walker not as a moderate but as one pandering to the far right.

Weeks later, as Walker prepared to declare his candidacy, his sons Matt, 21, and Alex, 20, told CNN they disagreed with his stance on gay marriage. Their mother had foreshadowed the family divide in an interview with the Washington Post.

“That was a hard one,” Tonette Walker had told the Post. "Our sons were disappointed.... I was torn. I have children who are very passionate [in favor of same-sex marriage], and Scott was on his side very passionate.”

Birthright citizenship must end

Trump, the billionaire businessman and front-runner for the GOP presidential nomination, brought the issue to the fore earlier this summer when he unveiled his immigration plan.

Several GOP hopefuls objected that ending birthright citizenship would require a constitutional amendment.

But Walker sided with Trump, who contends that a simple act of Congress would be enough to ensure that children born to mothers in the U.S. illegally would not be American citizens.

That wasn't the end of Walker's debate with himself, however. He flipped back and forth on the issue several times until eventually deciding he did not support ending birthright citizenship.

Many political observers viewed his shifting stances as amateurish. Questions began to rise about Walker's candidacy and whether he was ready for the national spotlight.

Build a wall along the U.S.-Canada border?

Walker said New Hampshire voters had asked him about putting up a wall at the Canadian border, and he was open to the idea.

His comment set off ridicule and raised eyebrows among Democrats and Republicans alike. Sen. Rand Paul of Kentucky called it a “dumb” idea. The Canadian Embassy in Washington issued a statement of objection.

To Republicans, securing the U.S.-Mexico border is vital for immigration reform, but the Canadian border doesn't inspire the same level of anxiety.

Walker ultimately was the odd man out on the issue, and soon backed down.

When it comes to the pope, presidential candidates tend to adopt a tone of deep reverence.

When it comes to Pope Francis, though, some Republican candidates are unusually eager to hit another note -- by pointing out where they disagree with the head of the Roman Catholic Church.

"I just think the pope is wrong," New Jersey Gov. Chris Christie said about the warming of relations between the U.S. and Cuba.

"The pope as an individual," said Florida Sen. Marco Rubio, "has political opinions. And those, of course, we are free to disagree with."

The question of papal infallibility comes up as Francis lands in the U.S. on Tuesday for the first time -- and as the presidential campaign veers sharply into the territory of religion. Dr. Ben Carson says Muslims shouldn't be president. Front-runner Donald Trump is questioning whether President Obama supports the religious liberties of Christians.

Christie and Rubio, both Catholic, are following in the historic footsteps of another prominent church member in public life. Before he was elected president, John F. Kennedy delivered a defining political speech declaring his independence from the pope.

No Catholic prelate would tell a Catholic president how to act, Kennedy said in September of 1960, just as no Protestant minister would tell his parishioners for whom to vote.

"I believe in an America that is officially neither Catholic, Protestant nor Jewish, where no public official either requests or accepts instructions on public policy from the pope, the National Council of Churches or any other ecclesiastical source," Kennedy said.

Of course, the current pope offers unusually political reasons for a conservative politicians to draw distinctions. He has helped the Obama administration negotiate with the Cuban government, called on Christians to fight climate change and urged prison reform, among other positions that also appear liberal by current American political standards.

But Christie and Rubio talked doctrine, not politics, in embracing their right to disagree.

The pope's infallibility "is on religious matters, not political ones," Christie told CNN's Jake Tapper.

Rubio said he follows the pope on doctrine.

"He's the spiritual head of the church, who has authority to speak on matters, doctrinal matters, and theological matters," Rubio told ABC's George Stephanopoulos. But "I have a job as a United States senator to act in the best interests of the United States and of our people, and from time to time, that may lead to different opinions about different things."

Other candidates have mostly kept a distance, though Republican Jeb Bush and his wife, Columba, are expected to attend Mass with the pope this week.

Real estate mogul Donald Trump, a Presbyterian, doesn't sound like he plans to meet the pope, though he's pretty sure it would turn out well.

"Well, I think if he knew me, I think he'd like me," Trump told NBC's Chuck Todd. "If he doesn't know me, perhaps he wouldn't. But if he knew me, I think he'd probably like me."