It's the day before a potential final vote on Republicans' tax bill, and Republicans are not having a good one.

A crucial GOP senator is raising questions about the bill after finding out that it includes a tax break that could financially benefit him and politically tarnish him.

Sen. Bob Corker (R-Tenn.) says he wasn't aware of this new tax break for wealthy real estate developers like him, but the left is whacking him for initially withholding support yet later backing the bill around the same time that this provision was included.

Corker, who is retiring next year, has denied he had anything to do with this provision. But if the senator feels that he can't vote for the final tax bill because of perception fears, the whole legislation could fall apart the same week that Republicans had hoped to finally pass it.

That might be fine with a majority of America. On Monday, a Monmouth University poll showed that Americans disapprove of the tax bill by a 2-to-1 margin. Just a quarter of Americans support this bill.

Hovering over all of this is the fact that Senate Republicans' margin for error just got much smaller. Sen. John McCain (R-Ariz.) has returned to his home state for an indefinite period as he receives treatment for brain cancer, which means that Republicans can afford only one “no” vote and have the final version of their tax bill pass.

At the 11th hour, Republicans' rushed, scrambled, sometimes chaotic effort to finish a tax bill by Christmas could be catching up to them. Republicans are racing to pass a tax bill that is unpopular with the masses, that was cobbled together with an arbitrary deadline and, as a result, at least has the appearance of shady legislative dealmaking.

“This bill was put together in a frenzy,” said Steve Bell, a former Senate GOP budget aide who is with the Bipartisan Policy Institute. He says Republicans have boxed themselves into a less-than-ideal legislative process. “They set up a public relations event — a Christmas present for America, Make America Great Again — and had to meet that deadline no matter what,” he said.

None of this means that the tax bill is doomed. Republicans have edged right up to the cliff lots of times throughout this months-long tax debate. It was touch-and-go on whether the Senate could pass its version of a tax bill earlier this month, but it did, as skeptical Republicans such as Corker flipped their vote to yes at the last minute. Passing the House's version with just Republican votes wasn't a cake walk, either.

But Republicans knew they had no choice but to try. As Sen. Lindsey O. Graham (R-S.C.) has said, “failure is not an option” for the Republican Party right now. If Republicans don't pass this bill, they will end their year in control of federal government without a single major legislative accomplishment. That doesn't set them up well for the 2018 midterm elections, in which Senate Democrats have a path to take back the majority, and House Democrats are equally optimistic.

Republicans are haunted by the failure of an Obamacare repeal bill this summer that was dogged by similar problems as those facing the tax bill: a partisan, rushed process that divided an already ideologically diverse caucus and let opponents define the legislation as bad for the middle class and good for the wealthy.

Speaking of public perception, versions of Republicans' Obamacare repeal bill polled in the teens. The tax bill isn't much more popular. As Republicans have focused all their energies on just trying to get the legislation passed, the Monmouth University poll shows that just 26 percent of Americans approve of the bill, while half believe their taxes would go up as a result of this legislation. That's similar to a November Washington Post-ABC News poll that found that a third of Americans support the bill, while half oppose it.

"The conference agreement (as well as prior versions of the bill) have been put together on an insanely fast timeline," said New York University professor Lily Batchelder, the deputy director of the White House National Economic Council under the Obama administration, "with virtually no opportunity for the public to seriously digest it and weigh in.”

Senate Republicans maintain that spending more time on this tax bill wouldn't help. It wouldn't bring Democrats on board, nor would it provide any groundbreaking consensus among wary Republicans. Plus, as time has gone on, the bill has become more unpopular with the public, so why wait?

Whatever the reason, Republicans are plowing ahead with this bill. And the rush comes at great risk, as they are relearning ahead of the looming vote.