President Donald Trump's choice to run the White House budget office Tuesday cleared a routine Senate hurdle. But at least two senior Republicans have voiced doubts about supporting him in Thursday's confirmation vote.

Rep. Mick Mulvaney is a tea party congressman from South Carolina who has attracted likely opposition from Armed Services Committee Chairman John McCain. McCain says Mulvaney's record of support for military operations in Afghanistan and the Pentagon budget generally is too soft.

The Senate voted 52-48 along party lines to advance Mulvaney to a final vote on Thursday, where the outcome is in greater doubt. McCain voted to advance Mulvaney to a final vote but again told reporters that he’s likely to oppose him.

Powerful Appropriations Committee Chairman Thad Cochran of Mississippi is also unwilling to commit to supporting Mulvaney in Thursday’s up-or-down vote. Cochran met with Mulvaney on Tuesday and is unwilling to commit to supporting him.

“He’s never been a friend of the Appropriations Committee,” Cochran said. “I don’t think he’s ever (liked) an appropriations bill.”

Since Democrats are unified against Mulvaney over his support of cutting Medicare spending and his past positions as a tea party firebrand in the House, only two Senate Republicans can defect if he is to be confirmed. If McCain and Cochran oppose Mulvaney on Thursday, Vice President Mike Pence would have to cast a tie-breaking vote to confirm him.

The Senate is moving slowly on Trump’s Cabinet. Majority Leader Mitch McConnell on Wednesday warned that continued delays are putting the chamber on course to “working well into the weekend.”

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