President Bush gave Bolton a recess appointment last year when Sen. George Voinovich, R-Ohio, refused to support the nomination in the Senate Foreign Relations Committee. Voinovich announced last week that he has had a change of heart.
But most Democrats still remain opposed to Bolton, The Washington Times reports.
"No, this is going to be a bruising fight," Sen. Christopher Dodd, D-Conn., said when asked on CNN if he now supports Bolton. "I regret this. I'm sorry the administration wants to go forward with this. The problems still persist."
Bolton himself told Fox News that he is optimistic about confirmation.
If Bolton is not confirmed, his appointment would expire in the fall. Debate in the Senate is scheduled this week.