As the Senate prepares to take up its version of a tax policy bill, with the potential of a vote by week’s end, Republicans look about eight votes short. The big question is whether those reluctant members will put aside their concerns in favor of party unity or demand major changes to the legislation, complicating its route to passage.

While the Senate vote is important, it’s not the final step before the tax policy overhaul goes to President Trump. The House passed a bill earlier this month that differs significantly from what the Senate is considering. Republicans need to get a bill through the Senate so that either the House can adopt the Senate version or the two chambers can set up a conference to reconcile their bills.

The vote count in the Senate seems fairly simple at this point. Fourteen Republicans already voted for the legislation when it was considered by the Senate Finance Committee, and 28 other members have either praised the bill or not yet publicly indicated any kind of serious disagreement.

That leaves 10 Republicans to watch, with Republicans needing to get support from at least eight of them. I’ve listed the members alphabetically except to link those with common concerns, particularly the large bloc of members focused on the effects of this bill on the federal budget deficit.

Maine’s Susan Collins has criticized the legislation for including a repeal of the individual mandate for purchasing health insurance, arguing that Republicans should leave health care out of this bill. She has also suggested that the bill cuts taxes on corporations too deeply and should instead put more money toward tax reductions for individuals. Also, Collins is the Senate Republican who most often votes against legislation backed by Trump and Senate GOP leadership, according to FiveThirtyEight’s Trump Score. Kansas’s Jerry Moran has also criticized the inclusion of the individual mandate.

Tennessee’s Bob Corker and Arizona’s Jeff Flake and John McCain have expressed concerns about the deficit growing under this legislation. (The Senate bill is currently estimated to increase the deficit by $1.4 trillion over the next 10 years.) Corker has gone the furthest of the three, saying that if “we are adding one penny to the deficit, I’m not going to be for it.”

The three men face no political pressure to back this legislation. Corker and Flake are not seeking re-election next year, while McCain’s brain cancer diagnosis means he is unlikely to run for another term in 2022. All of them have questioned Trump’s judgment, and Trump has returned the favor by attacking them in deeply personal terms. This trio can weaken a president they disdain by blocking the tax proposal he strongly supports and leaving him without a major legislative achievement in his first year.

Oklahoma’s James Lankford and Indiana’s Todd Young have said they, too, are worried that the Republican tax proposals increase the deficit too much — but they face some political pressure to get behind this bill. Unlike Corker, Flake and McCain, they are likely to seek re-election and are in states where Trump won overwhelmingly in 2016.

Wisconsin’s Ron Johnson says the legislation’s tax cuts unfairly favor large corporations over smaller businesses. Montana’s Steve Daines has similar concerns.

Alaska’s Lisa Murkowski actually defended the repeal of the health insurance mandate in an op-ed she wrote in an Alaska newspaper last week. But she remains a wild card. She, like Collins, is a regular dissenter from Trump and Senate leadership. And both of them, along with McCain, showed that they are willing to kill major GOP initiatives when they voted against Obamacare reform this summer.

With that many members wary of the legislation, there are two general paths this process can take. One path is that Senate Republican leaders and Trump, making the case for party unity, persuade the Senate GOP to get its bill passed as soon as possible, resolve any differences with the House quickly and send final legislation to Trump’s desk before Christmas.

In this path, the reluctant senators would accept minor changes to the legislation but largely put aside their concerns, particularly about the deficit. (Given the size of the current deficit projection, Republicans would otherwise have to make wholesale changes to win Corker’s support.) This path of minimal alterations would avoid the long (and ultimately unsuccessful) process from the attempt to repeal Obamacare, and it would deliver a big legislative victory to Trump and the party in the smoothest way possible.

In the second path, the senators don’t back down and instead demand major changes to the bill. This would, in contrast, resemble the Obamacare repeal effort in June and July, when party leaders tried to placate reluctant members. The challenge is that many of the policy goals of the nine potential holdouts contradict those of Republicans already on board. Arkansas’s Tom Cotton and Kentucky’s Rand Paul really want the repeal of the individual mandate in this legislation, even as Collins and Moran oppose it. Florida’s Marco Rubio wants this legislation to include more tax cuts for middle-income families and wouldn’t be happy if those currently in the bill are pared down to avoid increasing the deficit. And because the House must agree on a final bill, it’s worth noting that the House Freedom Caucus wants the corporate tax rate as low as possible and would oppose increasing that rate from the current 20 percent proposal to satisfy Collins.

This horse-trading could lead to a bill getting passed, and if the final result didn’t increase the deficit but did include tax cuts for the middle class, it could ultimately be a better political move for the Republicans. But it’s easy to imagine this unruly process extending into January or February, and Republicans in the Senate once again spending months fruitlessly trying to write a bill that gets 50 GOP senators behind it. As with Obamacare, such a failure would make congressional Republicans and Trump look disorganized and unable to govern despite having the presidency and both houses of Congress.

Trump could still receive a tax cut bill on his desk as his Christmas gift. Or his present for Presidents Day (which is Feb. 19). But there are enough rankled Republican senators that he should be worried the package might never make it to the White House.