In an implicit challenge to the candidacy of Donald Trump, the Republican National Committee asked candidates Wednesday to pledge they will not run as independents should they fail to win the nomination, a GOP campaign official said.

Trump, the reality television star turned Republican presidential front-runner, has toyed with the idea of running as an independent -- a move that could ultimately hurt the party as it seeks to capture the White House in 2016.

The document, from RNC Chairman Reince Priebus and first reported by Politico, asks campaigns the following:

"I ______ affirm that if I do not win the 2016 Republican nomination for president of the United States I will endorse the 2016 Republican presidential nominee regardless of who it is," the document says. "I further pledge that I will not seek to run as an independent or write-in candidate nor will I seek or accept the nomination for president of any other party."

During last month's debate, moderators asked candidates whether they could pledge to support whoever ultimately won the party's nomination for president, as well as rule out an independent bid, and Trump indicated he wouldn't.

"I want to win as the Republican. I want to run as the Republican nominee," he said. When pressed, Trump was direct, saying, "I will not make the pledge at this time."

Trump and Priebus are to meet Thursday at Trump Towers in New York, according to a Republican official. Trump is scheduled to hold a news conference in New York on Thursday.

They had a chopped salad. They talked about the middle class. And beyond that ...

Sen. Elizabeth Warren (D-Mass.) offered only a few details Wednesday of her recent meeting with Vice President Joe Biden, an encounter that sparked intrigue about his plans for the 2016 election and whether she might figure in them.

It was a "good, long, rambly policy conversation," Warren told the Boston Globe for its "Political Happy Hour" Web show. But when asked whether they talked about running together as a ticket, she repeated only that it was a "good conversation."

Warren said the origin of the meeting was simple. "He called me," she said. "He called me twice."

On the menu was what she described as a "chopped salad thing," though she couldn't quite remember what was in it. They talked about the "direction the country is going in" and the "capture of this country" by powerful, moneyed interests.

When asked whether she would commit to serving her full six-year term in the Senate, a pledge she made during her 2012 campaign, Warren demurred. "I love my job," she said. "It's all I'm thinking about."

Warren said she imagined she would endorse a candidate in the 2016 Democratic presidential primary, but that it was still early.

Early in his remarks at a community college in Florida on Wednesday, Vice President Joe Biden praised the “courage” it took for adults to return to school after years in the workforce.

“People who aren't willing to risk failing never succeed,” he said.

The comment may well indicate how Biden views a potential 2016 White House bid.

There are obvious challenges ahead, starting with the distinct advantage that Hillary Rodham Clinton has in raising money and building a campaign infrastructure not just in the early primary states, but across the country.

But the one way Biden, who has already run for president twice, could ensure he never reaches that long-held goal would be not to run at all.

The vice president's trip to Miami Dade College and other stops on his itinerary for the next two days are official administration and party business, not intended to be the kinds of waters-testing exercises you might expect.

And much of what Biden said Wednesday he's been saying for years, including when he quoted an Irish poet -- “The best poets,” he joked, again.

But what's always been true about a potential Biden candidacy is how easily his vice presidential duties could set him up to run. As Biden himself said years ago, everything he would need to do to be a candidate aligns with being a good vice president.

And what those in Biden's orbit see as his biggest asset in a potential campaign is how forcefully he can articulate what it means to be middle class, and how important it is to fight to preserve that way of life.

Under the leadership of President Obama, Biden said Wednesday, “we've gone from crisis to recovery, and now we're on the verge of a real resurgence in the American economy.”

“But what's not happened is, the middle class is not back yet,” he added.

He cited studies that found that the American middle class is no longer the wealthiest middle class in the world, and that fewer Americans believe that their children will be better off than them.

“We can't let that stand,” he said.

That's not to say Biden did not give some hints about 2016. He called economic inequality “the greatest threat to economic growth and stability.”

And as he defended administration plans such as the one for free community college, paid for through closing tax loopholes. He at one point spoke directly to the media on hand: “I can hardly wait, in the Congress or whatever forum, to debate my friends about [it].”

Biden's schedule on this swing has included a party fundraise and stops in Florida and Atlanta to help boost the proposed nuclear agreement with Iran.

On Monday, he's scheduled to engage in a more obvious political tradition -- participating in Labor Day festivities in Pittsburgh.

Martin O'Malley is sticking to his "debate the debate" strategy.

The former Maryland governor and Democratic presidential candidate is encouraging supporters to protest outside his own party's headquarters to draw attention to his complaints about the Democrats' primary debate schedule.

The O'Malley campaign sent an email to supporters Wednesday asking them to gather outside the Democratic National Committee headquarters in Washington on Sept. 16, the day of the second Republican primary debate in California.

Democrats aren't due to debate until Oct. 13, and O'Malley, whose struggling campaign could use the free exposure, argues that's too late.

"They malign our president's record of achievement; they denigrate women and immigrant families ... and, we respond? With crickets," O'Malley said last week at a DNC meeting in Minneapolis. O'Malley called the schedule "a cynical move to delay and limit our own party debates." He says the party has rigged the schedule to benefit front-runner Hillary Rodham Clinton.

Welcome to American politics -- 2016 edition.

The selfie is a craft that many White House hopefuls have had to master this election cycle.

And Sen. Rand Paul (R-Ky.) is taking it to a new level.

On Wednesday, his campaign released an app that allows supporters to take a selfie with the presidential candidate, even if they're not in the same room.

Supporters and journalists alike are using it.

Donald Trump took a first step toward trying to heal his rift with Latino voters.

The Republican presidentail candidate, who called some Mexican immigrants “rapists” in his campaign launch speech, met privately with the head of Hispanic Chamber of Commerce on Tuesday and promised to participate in the group's candidate forum next month, both parties said.

Trump's campaign requested the meeting with Hispanic Chamber Chief Executive Javier Palomarez, and the two met privately at Trump's offices in New York. They discussed Trump's immigration policies, trade and other issues, Palomarez said in interviews after the meeting.

Palomarez emphasized that he disagrees with Trump's plan to deport millions of immigrants living in the U.S. illegally. He said he told Trump that no candidate will win the White House without winning at least half the Latino vote.

“No candidate, man or woman, will see the White House without courting the Hispanic vote,” Palomarez told MSNBC's Chris Hayes.

Trump has a lot of catching up to do on that front. A Gallup analysis released last week showed 65% of Latinos have a negative view of the real estate magnate.

Trump will sit down for a 90-minute public interview with Palomarez on Oct. 8. in Washington.

Vice President Joe Biden is traveling this morning to a key presidential battleground where he will talk about two major campaign issues, meet with Democratic donors and try to smooth over relations with a key Democratic constituency.

But, no, this trip is not related to his deliberations on whether to run for president, his office says.

Biden's trip to Miami may not have been scheduled as a campaign test drive -- it's not unusual for the vice president to go on this sort of mission -- but given the speculation about his bid, it will be scrutinized like one.

The vice president's trip may offer a preview into what a Biden 2016 campaign stop might look like.

He will deliver remarks at the Science Center at Miami Dade College to talk about the Obama administration's job training initiative and college affordability. The former has been a platform for Biden to tour other campaign battlegrounds and to reach out to the working-class voters seen as his core base. The latter is a top-tier issue for the progressive wing of the party.

From there Biden, will attend a fundraiser for the Democratic Senatorial Campaign Committee at the home of developer Stephen Bittel.

On Thursday, Biden will meet with Jewish community leaders in Davie. The topic is his boss' nuclear agreement with Iran, a deal that for months has aggravated relations between Jewish voters, a reliable Democratic constituency, and the Obama administration. Biden will try to sell the deal and ease the tensions. The remarks would be a test of how he'd defend the administration as a candidate -- if he decides to become one.

No matter how he fares next year, Donald Trump's presidential campaign will be remembered for its remarkable use of free media to get out his message.

The Times' Stephen Battaglio has a close look at how Trump manages the media, even dictating the when, where and how of most of his TV interviews.

"On-camera sit-downs take place in the marble-walled atrium of the 58-story Trump Tower on Manhattan's Fifth Avenue, where his corporate office is located," Battaglio writes.

"All of the major TV news outlets have studios a few blocks away. But candidate Trump takes an elevator from his office down to the front section of a bar that bears his name. ... 'That's his TV area, and if you want to get him, that's where he'll do it,' according to one of several news producers and executives who described the arrangement to the Los Angeles Times. 'You can say no and not get him.'"

The debate criteria have changed, but now comes the big question: How will Carly Fiorina perform on the main debate stage?

Her strong performance last month during the so-called “happy hour” debate against the likes of George Pataki and Bobby Jindal -- lower-tier Republican presidential candidates who have managed to gain no traction with voters -- will be considerably different as she's flanked onstage by the caustic Donald Trump.

Fiorina's resume as chief executive of Hewlett-Packard, where she oversaw mass layoffs, is certainly going to be fair game. Moreover, she had run for political office in the past and her argument that she's a political outsider could be shot down by top-tier candidates like Trump and Ben Carson, who are true outsiders and have never run for elected office.

But while no one in the male-dominated Republican field has truly stepped forward to assail Fiorina, the lone woman seeking the party's nomination, several critics on the sideline have thrown jabs her way.

Conservative commentator Ann Coulter declared on a recent radio show that she despised Fiorina “with the hot, hot hate of a thousand suns,” castigating the candidate for her support of birthright citizenship.

For her part, Fiorina, has centered her attention while stumping through early-voting states on Hillary Rodham Clinton, the front-runner for the Democratic nomination. From the controversy surrounding the former secretary of State's personal email server to the 2012 attacks on a diplomatic compound in Benghazi, Libya -- these have been staples Fiorina has hit on while on the trail.

Still, attacking Clinton will not help Fiorina stand out in the Sept. 16 main debate, should she make it.

Instead, she'll have to challenge her male counterparts, which Fiorina has done -- especially when it comes to standing up for women.

To date, she has gone after Trump for his attacks against Fox News journalist Megyn Kelly, calling them “offensive.” Moreover, after Jeb Bush said he doesn't think the country needs “half a billion dollars for women's health issues,” Fiorina dismissed the statement as “foolish.”

“It's really disappointing when a front-runner gives the Democrats an ad and a talking point before he's even in the race,” she told reporters last month.

The Simi Valley debate will be Fiorina's opportunity to shine should she seize the moment.

“Thanks to you,” she tweeted to supporters late Tuesday. “We will be able to share our message of leadership with Republican voters on the main debate stage.”

Staff writer Seema Mehta contributed to this report.