A handful of Republican senators will have outsize influence on the GOP's legislative push to enact tax reform.
President Trump and Republican leaders can afford to lose only two Republican votes in the Senate and still pass legislation overhauling the tax code. While they hope to peel off a few Democratic votes, they cannot count on a Democrat to provide the deciding vote.
That puts an immense amount of power to shape the final bill at the desk of every member of the upper chamber. And several have indicated that they will use it or are expected to.
The Tennessee Republican who describes himself as a fiscal conservative, could complicate matters for other members of his party if the bill turns into something that would unambiguously cut federal revenue.
"If it looks like to me ... we're adding one penny to the deficit, I am not going to be for it, OK?" Corker said Sunday on NBC's "Meet the Press."
"I care deeply about deficits in our country and that is going to be one of the major thresholds on which I judge anything," Corker told reporters Monday.
In past years, Republican legislators who in other situations criticize the growing debt have demonstrated willingness to vote for large tax cuts.
Corker, however, is in a unique position because he already has announced he will not run for re-election in 2018.
He's not necessarily opposed to all tax cuts, though. He said Monday that he would favor a tax bill that cut revenue if a credible economic model suggested that it could generate enough economic growth to make up for those losses.
That stance puts pressure on the party to put together a plan that is pro-growth and isn't too big a net tax cut in the traditional scoring models.
Fresh off rejecting the Obamacare overhaul pushed by President Trump and his fellow Republicans, the Arizonan once again could prove to be a maverick on tax reform.
McCain was one of just two Republicans to vote against George W. Bush's first round of tax cuts in 2001. The other was Rhode Island Sen. Lincoln Chafee, who would go on to join the Democratic Party.
In 2003, McCain also supplied a GOP "no" vote on Bush's tax cuts, joined again by Chafee and Sen. Olympia Snowe of Maine. In both cases, McCain cited concerns about the tax cuts benefiting the wealthy more than the middle-class as reason to oppose them.
Later, while running for president and during former President Barack Obama's tenure, McCain would align in favor of the Bush-era tax rates.
Nevertheless, he retains the potential to cause complications for Senate Majority Mitch McConnell.
In recent weeks, he has emphasized his priority on moving legislation through regular order, allowing all members, including Democrats, a chance to weigh in.
After last week's introduction of the joint GOP tax reform framework, McCain put out a generally supportive press release. His office didn't respond to further inquiries about his intentions.
The Kentucky fiscal conservative vocally opposed the Graham-Cassidy Obamacare overhaul legislation on conservative grounds, arguing that it didn't constitute a true repeal of the Affordable Care Act because it kept most of its taxes.
So far, he has positioned himself as though he wants to play a similar role in the Republicans' tax reform effort.
On Monday, he joined in a Democratic criticism of the GOP tax framework, tweeting "This is a GOP tax plan?"
Previously, he criticized the strategy of offsetting tax rate cuts by eliminating an equal amount of deductions and loopholes. But that tradeoff could be necessary to gain the votes of fellow Republicans who say they are concerned about the debt, such as Corker.
The Maine Republican hasn't yet chimed in on tax reform, and her office didn't respond to an inquiry about how she views the Republican framework.
Nevertheless, conservatives worry that she won't back the plan that has the enthusiastic support of the House Freedom Caucus, based on her track record of votes opposing Obamacare replacement bills and other high-profile issues. Instead, if Republicans need her vote, they may need to alter the plan.
"She's a problem. Let's just be honest about that," said Jason Pye, vice president of legislative affairs for FreedomWorks, a free-market group. Collins, he noted, scores lower than some Democrats on the group's scorecard.