Senator John McCain said on Wednesday he is leaning against voting to confirm U.S. President Donald Trump's nominee to be White House budget director, Representative Mick Mulvaney.
A Senate vote on Mulvaney, a leading member of the conservative House Freedom Caucus who represents South Carolina, was expected on Thursday at 7 a.m.
Wavering support from McCain alone would not jeopardize Mulvaney's confirmation, but the Arizona senator and former presidential candidate could sway other Republicans. A Senate panel only narrowly backed the nominee earlier this month in a party-line vote.
Republicans have 52 of the 100 Senate seats and are able to approve Trump's nominees if they can hold together a majority.
McCain, who chairs the Senate Armed Services Committee that oversees defense spending, a massive part of the U.S. budget, told CNN he is concerned about Mulvaney's opposition to such spending.
CNN, citing sources familiar with the matter, said fellow Republican Senator Thad Cochran also shares those concerns and is not sure he can support Trump's nominee.
Democrats have criticized Mulvaney for taking a hard fiscal line on popular social programs and for not paying more than $15,000 in taxes in relation to a household employee until after he was nominated.
He has said he favors raising the Social Security retirement age to 70 and means-testing beneficiaries of the Medicare healthcare program. These positions have drawn the ire of Senator Bernie Sanders, an independent who caucuses with Democrats and sought the party's presidential nomination in 2016.
(Reporting by Richard Cowan and Susan Cornwell; Writing by Susan Heavey; Editing by Kevin Drawbaugh and David Gregorio)