“What I will not accept is a tax hike on the middle and upper middle class, sacrificing their paychecks on the altar of ‘reform,”’ Paul wrote in a Forbes op-ed.

Appeasing the Paul flank of the party means steeper tax cuts that could risk alienating the Corker wing by adding to the deficit. That’s the sort of tightrope Trump and his allies will have to walk to placate tension between competing factions among congressional Republicans. They have more breathing room in the House, where they can afford to lose 22 members and still pass a bill.

Two Mavericks

John McCain, the self-styled maverick who voted against Republican-pushed tax cuts in 2001 and 2003 due to deficit concerns, may also prove a difficult vote to corral. He demonstrated his willingness to deal Trump a defeat in the health-care debate, and he has said he’d like to see a regular-order process for a tax bill with bipartisanship.

A different kind of maverick may join the Senate before year’s end. Roy Moore, the party’s rabble-rousing Senate nominee in Alabama, is the front-runner to win a special election slated for Dec. 12.

The former state Supreme Court justice has staked out a hard-line position on taxes. His campaign website calls for the eliminating of income taxes and instead imposing a flat tax on goods and services purchased. If elected, he has vowed to go to war with Senate Majority Leader Mitch McConnell, prompting worries from leadership that he won’t be a team player.

Unlike Trump-endorsed incumbent Senator Luther Strange, whom he defeated, Moore has earned a reputation as someone who would make trouble in Washington. Last year, he was suspended for ordering judges to enforce the ban on same-sex marriage despite it being ruled unconstitutional.

Collins, Murkowski

Another challenge is Collins, the most moderate member of the GOP, who is expected to announce on Friday whether she’ll run for governor of Maine next year. Collins has previously voted against a repeal of the estate tax, one of Trump’s priorities. The loss of the state and local tax break also would hit Maine more than other states.

Last week, Collins declined to offer any thoughts on the unified framework. “It’s still a work in progress,” she said.