The Senate voted 52-48 on party lines to begin debate on the Republican tax bill, putting the Senate within striking distance of passing it. Several Republicans who have not committed to voting for the final bill, including Sens. Collins, McCain, Corker and Flake, voted in favor of moving ahead.

What's next: Republican leadership wants to pass the bill by the end of the week. There will be up to 20 hours of debate and votes on a series of amendments prior to the final vote. The House has already passed a different tax bill and, should the Senate pass its bill, they will have to agree on a compromise package.

What they're saying:

Asked how he would vote on the final bill, Sen. Ron Johnson told reporters, "I'm going to see what the other votes are."

Asked about potential changes, including a possible trigger to limit the deficit impact of the bill, Sen. John Kennedy said, "We're still talking. And we may be talking up until its time to vote on the bill." Kennedy said he'd prefer a trigger for spending cuts rather than tax increases.

The concerns of multiple senators have not fully been resolved: There's no agreement on the trigger for the budget hawks, no pay-for to partially keep the state and local tax deductions Sen. Collins wants, and no settled language on the changes for small businesses sought by Sens. Johnson and Daines.