Senate Majority Leader Mitch McConnell, R-Ky., said he is confident Sen. John McCain, R-Ariz., won't cast a vote opposing the GOP tax reform bill simply to defy President Trump, who supports the effort.

"I know John McCain well enough to know he's not gonna cast a vote on tax reform over how he may feel about the current occupant of the White House," McConnell told Fox News' Laura Ingraham on Wednesday.

McCain is one of a handful of GOP senators who could help torpedo the tax reform push in the Senate, which is supported by Trump, as Republicans only hold a 52-seat majority and can only stand two lose two votes. McCain has told reporters that he still doesn't know how he will vote.

The Senate did vote Wednesday to open debate on the legislation.

McCain, who has been a vocal critic of President Trump, opposed and ultimately helped kill the Republican effort to repeal Obamacare over the summer.