A small number of Republicans — fewer than 10 — will probably determine the fate of the Trump tax plan. The group includes five senators who have been independent enough in recent months to defy their party leaders, not just with words but actions, as well as a couple who may be newly willing to do so.

John McCain helped defeat the Republican health care bill, in protest of its secretive, rushed process. Susan Collins and Lisa Murkowski voted against the same bill because they believed that middle-class and poor families had a right to health care access. Jeff Flake and Bob Corker ended their Senate careers rather than fully submitting to Trumpism. Then there are the two showing new signs of independence: James Lankford of Oklahoma and Jerry Moran of Kansas.

The tax bill is a test of all of them. For progressives, the bill is an easy call. It’s a huge tax cut for the wealthy, partly paid for with middle-class tax increases. For the same reason, the bill is deeply unpopular with voters.

But the Republican senators are in a tough spot. They are philosophically conservative. They believe in low taxes and small government. They share this belief with their Republican colleagues, their political base back home and, yes, their donors.

Yet all of the potential swing senators have a problem: This tax bill also contains provisions that betray their stated principles.

For McCain, the principle is the Senate itself. His current term is probably his last, given his cancer diagnosis, and he has been making a righteous stand on the behalf of the Senate — that it should aspire to greatness rather than operating as a banana-republic legislature that rams through bills.

The tax bill violates that stand. Almost as an afterthought, it includes a major change to the health care system — the repeal of the individual mandate. The Senate has not held hearings where experts weighed the pros and cons, talked about unintended consequences and looked for (to quote a recent McCain speech) “compromises that each side criticize but also accept.”

For that matter, neither the House nor Senate has held serious hearings on any part of the tax plan. No other modern piece of major legislation has ever been so rushed — except for the health care bill that McCain doomed. Congressional leaders are rushing this bill because they know it’s unpopular, and their haste is making a mockery of the institution that McCain holds dear.

For Collins and Murkowski, the principle is health care. More specifically, it’s decent health care for the working-class families who dominate their home states of Maine and Alaska. The two of them were the most consistent Senate opponents of the bills this year that would have taken insurance away from millions.

Now the tax bill threatens to undo some of their good work.

The repeal of the mandate would create turmoil in insurance markets, because fewer healthy people would sign up for coverage, raising prices for everyone else. Collins opposes the measure for that reason, while Murkowski supports it if it’s paired with other measures to stabilize health markets. But those measures would need to be sweeping to make up for the damage.

Then there are Corker, Flake, Lankford and Moran. Their principle is the deficit. “We don’t want to increase the debt and deficit as a result of tax cuts,” Moran said. If the bill adds “one penny to the deficit,” Corker said, he wouldn’t support it.

The current Senate plan adds more than 100 trillion pennies to the deficit in the first decade, according to the official estimate. And that estimate is probably low, because the plan depends on a budgetary gimmick. The bill’s authors set the most popular tax cuts to expire, knowing that a future Congress may extend them. Corker and Flake have correctly called out this ruse. They and their colleagues would undermine any claim to fiscal conservatism if they voted for any bill that resembles the current one.

So what are the senators going to do?

I hope that they do not fold because doing so — doing what President Trump and Mitch McConnell want — is the easier political path. I dearly hope they do not follow the cynical tactics of a few of their colleagues who have made a show of opposing a Trump-backed bill only to change positions after being offered a fig leaf of change. Senator Ron Johnson of Wisconsin and Representative Tom MacArthur of New Jersey have each done so more than once this year, and now it’s hard to take either seriously.

None of us should expect senators to vote only for bills that we personally support. They have their own beliefs and principles. But I do think it’s fair to expect them to vote only for bills that are consistent with those principles. This tax bill is not — not even close.