US United Nations Ambassador Susan Rice speaks during a Security Council meeting on the situation in Syria, August 30, 2012 at United Nations Headquarters in New York. (Getty Images)
WASHINGTON -- Embattled U.N. envoy Susan Rice is dropping out of the running to be the next secretary of state after months of criticism over her Benghazi comments, she told NBC News on Thursday.
"If nominated, I am now convinced that the confirmation process would be lengthy, disruptive and costly - to you and to our most pressing national and international priorities," Rice wrote in a letter to President Obama, saying she's saddened by the partisan politics surrounding her prospects.
"That trade-off is simply not worth it to our country...Therefore, I respectfully request that you no longer consider my candidacy at this time," she wrote in the letter obtained by NBC News.
Brian Williams will have an exclusive interview with Rice on Thursday night's "Rock Center With Brian Williams" at 10 p.m. on 11Alive.
Rice had been viewed as one of the front-runners to replace Hillary Clinton as the nation's top foreign policy official.
She has been under intense fire from Republicans for initially characterizing the Sept. 11 assault on the U.S. consulate in Benghazi, Libya, as a spur-of-the-moment response to a crude anti-Muslim film.
"What happened in Benghazi was in fact initially a spontaneous reaction to what had just transpired hours before in Cairo, almost a copycat of the demonstrations against our facility in Cairo, which were prompted, of course, by the video," Rice said on NBC's "Meet the Press" five days after the attack.
"Opportunistic extremist elements came to the consulate as this was unfolding. They came with heavy weapons, which unfortunately are readily available in post-revolutionary Libya, and it escalated into a much more violent episode."
As more details emerged suggesting it was a premeditated terrorist action, GOP critics accused Rice of misleading the public at the height of the presidential campaign.
She countered that she went with the best information available about the attack, in which Ambassador Chris Stevens and three other Americans were killed.
"I relied solely and squarely on the information provided to me by the intelligence community. I made clear that the information was preliminary and that our investigations would give us the definitive answers," she said on Nov. 21 at the United Nations.
By then, Obama had already expressed strong support for Rice, warning Sens. John McCain (R-Ariz.) and Lindsay Graham (R-S.C.) to stop slamming her and vowing to block her confirmation.
"They should go after me," he said at his first press conference after his re-election.
And last week, Clinton praised Rice as a "stalwart colleague" who had done a "good job" at the U.N.
Despite a series of closed-door meeting with Capitol Hill lawmakers to drum up support, Rice continued to face questions from senators key to her confirmation.
After a Nov. 28 sitdown with Rice, Sen. Susan Collins (R-Maine) said she couldn't yet endorse the veteran diplomat and raised a new point of concern: her role in protecting American embassies in Kenya and Nairobi that were bombed by terrorists in 1998.
Sen. Bob Corker (R-Tenn.) suggested Rice was seen as too much of an Obama loyalist and the GOP preferred "someone of independence."
In her letter to Obama, Rice took aim at her GOP critics.
"The position of secretary of state should never be politicized," she wrote, adding, "I'm saddened that we have reached this point, even before you have decided whom to nominate. We cannot afford such an irresponsible distraction from the most pressing issues facing the American people."
Her withdrawal leaves Sen. John Kerry (D-Mass.) as a possible candidate for the job, and Republicans have said he would have a smoother run.
"I think John Kerry would be an excellent appointment and would be easily confirmed by his colleagues," Collins said last month.