Senate Republican leaders continue to get support for their tax overhaul package, even though the details of what the chamber will vote on are still being worked out and despite the unlikelihood of significant changes before a potential conference with the House. 

Three Republican senators continue to call for a higher corporate tax rate to offset greater benefits for individuals in the tax measure, but GOP leaders are casting doubts on whether any such changes would be made prior to a conference.

Still, despite the continued lobbying by some Republican members, the bill appears to be moving in a positive direction for the GOP.

Sen. John McCain came out in support of the measure Thursday, ending speculation that the Arizona Republican might once again buck party leadership as he did with the recent health care effort.

Senate Majority Leader Mitch McConnell predicted at a press conference earlier in the day that the chamber would have a final vote on the bill either Thursday evening or Friday morning. But there is still a ways to go, and members continue to advocate for inclusion of their own amendments.

McConnell: Tax Bill a ‘Once in a Generation Opportunity’

Sens. Susan Collins of Maine, Marco Rubio of Florida and Mike Lee of Utah are all pushing amendments to raise the corporate tax rate above the proposed 20 percent. The increase could help pay for an enhanced child tax credit or the inclusion of a provision to allow individuals to deduct up to $10,000 in property taxes.

But those changes appear unlikely, as GOP leaders say any increase in the corporate rate is better addressed in an expected policy conference with the House.

“There are some concerns about raising the corporate tax rate right out of the box,” Senate Majority Whip John Cornyn of Texas said. “The most appropriate place to deal with that is in a conference, where there is a little bit of certainty about where we need to move things around.”

Those thoughts were echoed by Senate Republican Conference Vice-Chairman Roy Blunt.

“If it’s raised, my guess would be it’s raised to accommodate the conference differences between the House and Senate,” the Missouri Republican said.

Whether those three members would choose to oppose the bill without their suggested changes is an open question. Collins told reporters at the Christian Science Monitor breakfast on Thursday she needs to see a final package before deciding, citing the uncertainty of the process for the fast-track budget procedure known as reconciliation.

“Who knows what’s going to happen on the Senate floor during the vote-a-rama,” Collins said. “I need to wait to see what happens.”

Republicans can afford to lose the support of only two members, assuming that Vice President Mike Pence casts the tie-breaking vote. But with McCain on board, they are breathing a little easier.