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Up until this week, the White House was still privately challenging the record of Rice’s opponents on similar GOP nominations. In Congress, Democrats were more troubled by a steady drip of reports about Rice, from a possible conflict of interest over personal holdings and the Keystone XL pipeline to increased scrutiny about her relationship with the president of Rwanda and the country’s backing of a rebel group in Congo, a charge Rwanda denies.

In a letter to Obama, Rice bowed out, saying that “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. That trade-off is simply not worth it to our country.”

She added that she was saddened by the partisanship even before Obama made a nomination, but the country “cannot afford such an irresponsible distraction from the most pressing issues facing the American people.”

Obama bemoaned the relentless Republican criticism in accepting Rice’s decision to step aside.

“While I deeply regret the unfair and misleading attacks on Susan Rice in recent weeks, her decision demonstrates the strength of her character,” the president said.

Kerry is no stranger to the politicization of national security; he was the target of unsubstantiated claims by the Swift Boat Veterans for Truth over his Vietnam record. He acknowledged that experience in his statement Thursday praising Rice.

“As someone who has weathered my share of political attacks and understands on a personal level just how difficult politics can be, I’ve felt for her throughout these last difficult weeks, but I also know that she will continue to serve with great passion and distinction,” he said in a statement.

Tennessee Sen. Bob Corker, who will be the top Republican on the Foreign Relations Committee next year, applauded Rice “for making the right decision to withdraw herself, recognizing the atmosphere and damage a messy confirmation process would cause.”

McCain, Graham, Ayotte and Collins said in statements that they respected Rice’s decision while vowing to press ahead in getting answers about the Benghazi attack.

The White House said Rice would remain U.N. ambassador. She could become national security adviser should Tom Donilon move on to another position, though that is not expected imminently. The security adviser position would not require Senate confirmation.

Associated Press writers Ben Feller and Julie Pace contributed to this report.