President Barack Obama will nominate former Republican Senator Chuck Hagel to be his defense secretary and an announcement could come on Monday, sources familiar with the nomination process said.

The choice will likely set up a confirmation battle in the Senate over whether the former Nebraska senator and Vietnam veteran is a strong enough supporter of key U.S. ally Israel and over his past calls for military cuts.

The Obama administration backed down from a tough Senate confirmation battle over Susan Rice, the U.S. Ambassador to the United Nations, who was Obama’s first pick to replace Hillary Clinton as secretary of state.

Rice withdrew her name from consideration after drawing heavy fire from Republicans for remarks she made in the aftermath of a September 11 attack on the U.S. mission in Benghazi, Libya. Obama then nominated Massachusetts Democratic Senator John Kerry, a former presidential candidate.

“The administration has a lot of work to do on Hagel,” a Democratic Senate aide said on Sunday.

“He is in a weaker position now than Rice ever was because Rice would have rallied Democrats behind her. The administration floated Hagel’s name, then neglected to defend him effectively when his critics started taking shots,” the aide said.