Is Sen. Tom Cotton new conservative hero or just latest rabble-rouser?

Gone apparently are the days when newly elected senators followed the tried-and-true tradition of being seen, not heard, as they deferred to more-seasoned colleagues and learned the ropes.

After writing a controversial letter to Iran’s leaders early this week warning them against signing a deal with the Obama administration regarding their nuclear program, freshman Sen. Tom Cotton of Arkansas has become the latest congressional newbie to grab the national spotlight.

Conservatives heralded the Harvard-educated former Army infantry officer as their new hero, praising him for standing up to President Obama and reasserting Republican influence over national security.

But the letter, signed by 46 of Cotton’s fellow senators, triggered a backlash from the White House, liberals and even some in his own party. Critics call Cotton the latest conservative rabble-rouser who crossed a partisan line — bordering on treason, some left-leaning pundits say — by seeking to undermine the president’s authority in a sensitive negotiation with a foreign nation.

Some see Cotton as following in the footsteps of Sen. Ted Cruz. What the firebrand Texas Republican has done for domestic policy — asserting himself as a “disruptive” force unafraid to push boundaries — Cotton appears poised to do in foreign affairs.

And as is often seen with some of Cruz’s tactics — which have included prodding colleagues toward a strategy that resulted in a 16-day government shutdown in 2013 to protest Obama’s healthcare law — Cotton’s letter so far has heightened his personal standing even as his party has taken some heat.

Veteran defense hawk Sen. John McCain (R-Ariz.), chairman of the Armed Services Committee and one of the signatories, acknowledged Tuesday on Fox News that perhaps the message could have been sent to Iran in a way that wasn’t perceived as undermining the White House.

“Maybe that wasn’t exactly the best way to do that,” McCain said. “But I think the Iranians should know that the Congress of the United States has to play a role.”

The one-page message, addressed as an “open letter to the leaders of the Islamic Republic of Iran,” warned Tehran that any deal it reached with Obama could be revoked by the next president unless Congress approved it.

It was the latest move by Republicans, who have been increasingly skeptical of the president’s attempts to reach a deal to lift some international sanctions against Iran in exchange for limitations to ensure its nuclear program is used for peaceful purposes.

Cotton, an Iraq war veteran who handily ousted incumbent Democratic Sen. Mark Pryor in November, says he has no regrets.

“I will never apologize for standing for a safe and secure America!” he tweeted Wednesday. On Thursday he added: “I’ll always stand against a course of action that I believe is wrong and dangerous for America.”

In addition to accolades from conservative pundits, some are talking about Cotton as a future presidential aspirant. In Arkansas this week, supporters moved to change a state law to allow Cotton to run for both the Senate and the White House in 2020.

During his campaign last year, Cotton highlighted his military service. One ad ended with the image of an Army boot footprint, and he sometimes traveled the state in a camouflage bus.

At a Senate Armed Services Committee hearing earlier this year, Cotton said the military detention center at Guantanamo Bay, Cuba, should not be closed, as the president has sought, and that prisoners there, for

all he cared, could “rot in hell.”

That Cotton, the Senate’s youngest member, persuaded 46 Republican colleagues to join him — including GOP leadership — says much about the ambitious senator’s ascent.

“Sen. Cotton is already making a big difference,” said a fundraising appeal Wednesday from Florida Sen. Marco Rubio’s Reclaim America PAC, which backed Cotton’s fall campaign. The group noted that Rubio — a potential presidential contender in 2016 — was among the first Republicans to sign the letter.

“The key will be if [Cotton] can turn his new high-profile maverick status into something more, focusing in on a few important issues and serving as a coalition builder among Republicans,” said Princeton University history professor Julian E. Zelizer. “If not, it would be easy for him to go the route of trouble-maker in chief, which is fine for getting headlines, but not always the best path toward being a power broker in the Senate.”

Enthusiasm for Cotton’s approach has waned in the days since the letter’s release. Several of the Senate’s more pragmatic Republicans refused to sign on.

The White House called the letter reckless. Secretary of State John F. Kerry said Wednesday he was in “utter disbelief.”

The Iranian foreign minister dismissed it as “propaganda,” and on Thursday, Iran’s supreme leader, Ayatollah Ali Khamenei, said it showed the “internal disintegration” of the U.S. political system.

But conservatives’ support for the letter speaks to the GOP’s increasing willingness to challenge the president on foreign policy. It followed this month’s divisive invitation for Israeli Prime Minister Benjamin Netanyahu to address a joint meeting of Congress and speak against the Obama administration’s policy on Iran.

Cotton’s fellow military veteran Sen. Joni Ernst (R-Iowa), an Army Reservist who served in Iraq and who delivered the GOP response to Obama’s State of the Union address this year, said Thursday that “of course” she stood by her decision to sign the letter.

Another freshman, Sen. Cory Gardner (R-Colo.), brushed off the criticism, saying the letter accomplished its intent.

“This letter is about making sure the Iranian regime knows Congress will not stand for a bad deal, and I think the president has listened, learned and has acted,” Gardner said.

QUIZ: Who said it? Cotton, Cruz or Bachman

Special correspondent Ramin Mostaghim in Tehran contributed to this report.