Hagel, a decorated Vietnam veteran, would replace Leon Panetta at the Pentagon. Critics have already launched attacks over Hagel's record on Israel and Iran.
Brennan is a CIA veteran who withdrew from consideration for the spy agency's top job in 2008 after questions were raised about his views on enhanced interrogation techniques used on terrorism suspects during the Bush administration.
He would succeed retired General David Petraeus, who resigned amid a scandal over an extramarital affair with his biographer.
Since his name emerged last year as a candidate for the Pentagon, some Republicans contend that Hagel has at times opposed Israel’s interests. His critics note that he voted against U.S. sanctions on Iran, and made disparaging remarks about the influence of what he called a “Jewish lobby” in Washington.
The top Republican in the Senate, Mitch McConnell, praised Hagel when he left his Nebraska seat in 2009 for his “clear voice and stature on national security and foreign policy,” but his tone was markedly different on Sunday.
“He ought to be given a fair hearing like any other nominee, and he will be,” McConnell told ABC. “I’m going to wait and see how the hearings go, and whether Chuck’s views square with the job he would be nominated to do.”
But on CNN, leading Republican Senator Lindsey Graham did not shy away from a full-frontal attack, saying Hagel would be “the most antagonistic defense secretary towards the state of Israel in our nation’s history.
“Not only has he said you should directly negotiate with Iran, sanctions won’t work, that Israel must negotiate with Hamas, an organization, terrorist group, that lobs thousands of rockets into Israel.
“He also was one of 12 senators who refused to sign a letter to the European Union trying to designate Hezbollah as a terrorist organization,” Graham said.
Four years ago, Obama said Iraq was not the only matter where he held similar views with Hagel, a decorated Vietnam veteran who was also once touted as presidential material.
“He’s a staunch Republican, but Chuck and I agree almost on every item of foreign policy,” Obama said in August 2008, a month after taking Hagel with him on a tour of Iraq.
Hagel has also been critical of the size of the American military, telling the Financial Times in 2011 that the Defense Department was “bloated” and needed “to be pared down.”
Hagel served two terms in the Senate, representing the state of Nebraska, and left in 2008. He is now a professor at Georgetown University, but also serves as co-chairman of the President’s Intelligence Advisory Board, and a member of the Secretary of Defense’s Policy Board.