(CNN) -- Susan Rice, the U.S. ambassador to the United Nations who drew heavy criticism from Republicans over her statements after the September attacks on a U.S. diplomatic mission, withdrew her name from consideration for secretary of state on Thursday.
In a letter to President Barack Obama, she said "the confirmation process would be lengthy, disruptive, and costly -- to you and to our most pressing national and international priorities. That trade-off is simply not worth it to our country."
Obama acknowledged her letter in a statement that described her as "an extraordinarily capable, patriotic, and passionate public servant."
She was thought to be a frontrunner for the post, which Secretary of State Hillary Clinton said she would vacate as soon as a successor is confirmed.
But Rice drew criticism for her description of the September 11, 2012, attack on the U.S. mission in Benghazi, Libya, which killed four including the U.S. Ambassador to Libya, Chris Stevens. On several television programs several days after the attack, she described a protest of an anti-Islam video outside the mission buildings.
She said her comments were based on declassified talking points, and sources within the intelligence community said the talking points were not modified by any other body, such as the White House.
Obama had defended her, describing the criticism from several key Republicans as "outrageous." "If Senator McCain and Senator (Lindsey) Graham and others want to go after someone, they should go after me," Obama said at a White House news conference in late November. "When they go after the U.N. ambassador, apparently because they think she's an easy target, then they've got a problem with me."
She visited Capitol Hill in an attempt to answer what the legislators called "unanswered questions," but her visit there appeared to backfire. Senators who sat in on the meetings said her appearances raised more questions than they answered.
Her closed-door meetings "really hurt her," one knowledgeable Democratic source said. "She probably underestimated the club."
The longer Rice went un-nominated, the source said, the worse her prospects appeared. It was "better to get out now" so that Obama could begin announcing a national security slate as early as next week.
Rice's decision to not seek the post now leaves Sen. John Kerry, D-Massachusetts, as the presumed frontrunner for the spot. Defense Secretary Leon Panetta is also expected to depart his post soon.
Kerry's road to the State Department, should he be nominated, would appear to be smoother than Rice's. Senate Minority Leader Mitch McConnell said after Rice's announcement that Kerry would be a "popular choice with the Senate."
Another Senate Republican, Rob Portman of Ohio, named Kerry as one of Obama's "better choices" for the spot, according to The New York Times.
But despite his lauded role assisting Obama in preparing for the presidential debates this fall, Kerry is understood to be less of an Obama confidante than Rice.
Kerry is a decorated veteran who served two tours of duty in Vietnam before his career as a lawyer and then in the U.S. Senate. His assignments there include the chairmanship of the Foreign Relations Committee.
After Rice's Thursday announcement, Graham said in a statement: "I respect Ambassador Rice's decision. President Obama has many talented people to choose from to serve as our next secretary of state."
"When it comes to Benghazi, I am determined to find out what happened -- before, during, and after the attack," he continued. "Unfortunately, the White House and other agencies are stonewalling when it comes to providing the relevant information. I find this unacceptable."
The Thursday decision was Rice's own; she was not asked to step aside in the consideration process, a former administration official who had knowledge of her decision said.
"She has got a lot of honor, a lot of dignity, a lot of patriotism. This was a completely manufactured distraction, and she was determined to put her country first," the former official said. "No nominee for secretary of state has been subjected to such a sustained campaign of politicization and slander. And it is really troubling."
In her letter to Obama, Rice wrote "the position of secretary of state should never be politicized."
"As someone who grew up in an era of comparative bipartisanship and as a sitting U.S. national security official who has served in two U.S. administrations, I am saddened that we have reached this point, even before you have decided whom to nominate," she wrote. "We can not afford such an irresponsible distraction from the most pressing issues facing the American people."
Rice served in the Clinton administration on the National Security Council, eventually leading African affairs for the council and serving as a special assistant to the president.
She was confirmed by the Senate as the top diplomat to the U.N. in January 2009.
If Rice had been nominated, she would have faced criticism from religious leaders about her role in the Clinton administration's handling of the Rwandan genocide in the 1990s.
U.S. Rep. Mike Rogers, chairman of the Permanent Select Committee on Intelligence, said on CNN after the announcement that it was "probably for the best."
"I think Ambassador Rice was facing an uphill battle in the senate for any confirmation she may have received," he said.
-- CNN's Jessica Yellin, Jim Acosta, Dana Bash, Gloria Borger, Elise Labott, Jamie Crawford and Gregory Wallace contributed to this report
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