Moderate Republican Sen. Susan Collins met with Susan Rice on Wednesday and afterward said she could not support her for secretary of state without more information, raising a new concern about the U.S. Ambassador to the United Nations.
Other Republicans have threatened to block Rice's nomination if President Barack Obama picks her to replace Hillary Clinton, which would require Senate confirmation.
Votes from moderate Republicans like Collins would be needed to overcome procedural obstacles.
"I still have many questions that remain unanswered," Collins told reporters after a 75 minute meeting with Rice.
Collins said she still wanted more information about the Sept. 11 attack on the U.S. mission and a nearby CIA annex in Benghazi, Libya in which the U.S. ambassador and three other Americans were killed.
The Maine senator voiced a new concern about Rice after the meeting, stressing that the United States seems not to have learned lessons from the 1998 bombings of U.S. embassies in Africa, when Rice was the State Department's Africa region head.
Collins said this year's attack in Benghazi "echoed" the attacks on the embassies in Kenya and Tanzania 14 years ago. "In both cases, the ambassador begged for additional security," and both requests were turned down by State, she said.
"I asked Ambassador Rice what her role was. She said that she would have to refresh her memory but that she was not involved directly in turning down the request. But surely, given her position as assistant secretary for African Affairs, she had to have been aware," Collins said.
Some senators have openly criticized Rice for initial comments after the Benghazi attack that suggested it was a spontaneous event arising from protests of an anti-Islam film rather than a pre planned terrorist strike.
Intelligence officials later said the attack was possibly tied to al-Qaida affiliates.
Republicans have argued that the Obama administration tried to play down the terrorist angle in its initial comments to avoid undermining the president's claims of success in fighting al-Qaida in the run-up to the Nov. 6 election.
Collins, the top Republican on the Senate Homeland Security Committee, said she was concerned over Rice playing what she termed a "political role" by appearing on television to comment on Benghazi at the height of a contested presidential campaign.
Rice, accompanied by acting CIA Director Michael Morell, also met with Sen. Bob Corker, who is line to be the top Republican on the Senate Foreign Relations Committee, after her discussion with Collins.
After his meeting, Corker had tough words for the Benghazi attack and the aftermath, which he termed a "tawdry affair," that would add to Americans' distrust of the government.
"I am very disappointed in the entire apparatus here," Corker told reporters.
He declined to discuss whether he would support Rice, but urged Obama to "step back" from the controversy surrounding Rice and "take a deep breath" as he decided who to nominate as secretary of state.
"When he makes that nomination, I look forward to thoroughly examining that person, looking at their credentials and making my own determination at that time," Corker said.
It was Rice's second straight day of meetings at the U.S. Capitol.
The U.S. ambassador to the United Nations met for about an hour behind closed doors at the Capitol on Tuesday with Republican Sens. John McCain, Lindsey Graham and Kelly Ayotte, who have been vocal critics of Rice.
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