 -- Sen. John McCain, R-Ariz., gave a boost to efforts by President Donald Trump and Republican senators to get a tax reform bill through Congress Thursday, but a late push from deficit opponents has the bill in limbo Friday.

Voting on the bill was called off Thursday night, with Senate Republicans set to make changes overnight. The plan is to resume votes on Friday at 11 a.m., though it's not clear what the bill will look like then.

Sen. Bob Corker, R-Tenn., wants more revenue, somewhere around $350 billion to be exact, because he doesn’t like how much this bill increases the deficit. The only way to get that kind of revenue was to fundamentally reshape this bill, just hours before it was supposed to get a vote on the Senate floor.

Earlier in the day Thursday, McCain, who has become a thorn in Trump's side in recent votes, said he would support the tax bill.

“After careful thought and consideration, I have decided to support the Senate tax reform bill,” McCain said in a statement. “I believe this legislation, though far from perfect, would enhance American competitiveness, boost the economy, and provide long overdue tax relief for middle class families.”

McCain’s support came at a critical time for the measure.

The Senate voted to proceed to debate on the bill on Wednesday, giving Republicans a procedural win. But it’s still unclear whether Sen. Majority Leader Mitch McConnell will have enough votes to pass the bill as differences continue to be hammered on the Senate floor. Sen. Ron Johnson, R-Wis., Sen. Lisa Murkowski, R-Alaska, and Sen. Susan Collins, R-Maine, among others, have expressed concerns over the legislation.

President Trump and Republican supporters are pitching the measure as a tax bill for the working class, not the wealthy. Trump told his supporters at a speech in Missouri yesterday, "It's going to cost me a fortune."

It is unclear how the bill would affect the president personally without his tax returns being made public.

McCain on Thursday added to the sentiment that this was a measure for the working class.

“This bill would directly benefit all Americans, allowing them to keep a higher percentage of what they earn,” he said in his statement adding that lowering the corporate tax rate to 20 percent would make U.S. markets more attractive for investment.

According to the Congressional Budget Office, the bill would increase the national deficit by $1.4 trillion over the next decade and disproportionately hit lower-income taxpayers.

Some of the measure’s critics also point to the inclusion of a repeal of the 2010 Affordable Care Act’s individual mandate. The mandate requires that all Americans with the ability to pay for health insurance purchase it.

The CBO predicts that if the legislation to repeal the mandate is enacted, the number of people with coverage would drop by 4 million individuals in 2019 and 13 million in 2027. Average premiums in the insurance marketplace would increase by roughly 10 percent each year when compared to estimates under existing law.

McCain supports including a repeal.

“As a matter of principle, I’ve always supported individual liberty and believe the federal government should not penalize Americans who cannot afford to purchase expensive health insurance,” he said in the statement.

The Arizona senator voted with Democrats in late July to defeat the Republican effort to dismantle the Affordable Care Act. His lack of support tanked a revived effort at repeal in September.

But on tax reform, McCain is now poised to help Republicans clinch what they hope is a key legislative achievement ahead of the 2018 midterms.