Defence Secretary nominee Chuck Hagel has sought to allay concerns that he is anti-Israel and soft on Iran, at a testy confirmation hearing.
The Senate armed services committee grilled Mr Hagel over his past remarks, with a fellow Republican labelling the nominee's record "deeply troubling".
The former Nebraska senator told the panel he could not be defined by any individual quote.
The hearing will lead to a final Senate vote on Mr Hagel's appointment.
Correspondents say he will probably be confirmed by the committee.
Although Democrats control the Senate, they may need Republican support to overcome procedural hurdles that could stop Mr Hagel's nomination.
Charm offensive
If confiAt Thursday's public hearing, Mr Hagel said he was "fully committed" to preventing Iran from obtaining a nuclear weapon, with "all options" on the table.
"I will ensure our friend and ally Israel maintains its qualitative military edge in the region," he added.
Mr Hagel also addressed criticism over a remark he made in a 2008 book that the "Jewish lobby" intimidates decision-makers on Capitol Hill.
"I've already said, I regret referencing the Jewish lobby," he told the hearing. "I should have said the pro-Israeli lobby."
Mr Hagel would be the only Republican in President Barack Obama's cabinet if the Senate confirms him to replace outgoing Defence Secretary Leon Panetta.
Before his hearing, he held one-on-one meetings with 53 senators.
But only one Republican senator, Thad Cochran of Mississippi, has publicly backed him.
Once the hearing was under way, the Republican National Committee sent a news release saying Mr Hagel was the wrong choice to lead the Pentagon.
At least three Republicans on the Senate armed services committee have said they do not support his nomination.
Heated exchange
One of those is Senator Jim Inhofe, the top Republican on the panel, who said shortly after the hearing began: "Senator Hagel's record is deeply troubling and out of the mainstream."
There was also a heated exchange between John McCain and the Pentagon nominee.
The Arizona senator took his fellow veteran to task over remarks he made once that the 2006 Iraq troop surge would be "the most dangerous foreign policy blunder in this country since Vietnam".But Democratic Senator Carl Levin, chairman of the committee, said his concerns had been allayed.
"Senator Hagel's reassurance to me," Sen Levin said, "that he supports the Obama administration's strong stance against Iran is significant."
The hearing is the first time Mr Hagel has publicly addressed the criticism against him.
In the past, he has opposed the idea of a military strike by either the US or Israel against Iran. He has also advocated including Iran on future peace talks in Afghanistan.
His remarks in 1998 that a nominee for an ambassadorial post was "openly, aggressively gay" also raised eyebrows. Mr Hagel has since apologised for that comment.rmed, he would be the first enlisted man - and the first Vietnam veteran - to run the Pentagon.
