Republicans spent the day scrambling to reformulate the bill, which aims to cut taxes on corporations, other businesses and many individuals and families, to satisfy lawmakers worried about how much it would balloon the U.S. budget deficit.

Stocks rallied on optimism it could pass, but obstacles remained, including attempts to address the estimated $1.4 trillion that the bill would add to the United States’ $20 trillion national debt over 10 years.

Lawmakers voted 52-48 to begin formal debate, a step that could lead on Thursday and Friday to a full vote on the bill. Republicans are eager to pass the legislation, wanting something to show for their control of the White House and both houses of Congress.

Republicans have a 52-48 majority in the 100-member Senate, giving them enough votes to approve the bill if they can hold together. Without Democratic support, Republicans can afford to lose no more than two of their own votes.

President Donald Trump in a speech in Missouri on Wednesday, implored members of his own party to get behind the effort, which would be his first significant legislative achievement since taking office in January.

“A vote to cut taxes is a vote to put America first again,” Trump said, adding the bill could “cost me a fortune” and that his wealthy friends were not happy. “My accountants are going crazy right now. It’s all right. Hey look, I am president, I don’t care. I don’t care anymore.”

Democrats say the tax cuts are a giveaway to corporations and the wealthy at the expense of working Americans. Some Democrats have said Trump and his children would gain from the bill, which would repeal the estate tax on inherited wealth.

Among Americans aware of the Republican tax plan, 49 percent said they were opposed, up from 41 percent in October, according to a Nov. 23-27 Reuters/Ipsos poll released on Wednesday. The latest online poll of 1,257 adults found 29 percent supporting the plan and 22 percent saying they “don’t know.”

The sweeping tax package was developed over several months behind closed doors by a small group of senior congressional and Trump administration figures, with little input from many Republican lawmakers and no involvement from Democrats.

A major sticking point in the Senate is how the bill deals with the federal deficit and the national debt.

Senator Bob Corker, one of the few remaining fiscal hawks in the Republican Party, wants to add a tax snap-back provision to the bill that would raise taxes automatically if economic growth targets are not hit in the future to offset a higher deficit.

That trigger proposal has become a target of growing criticism among conservative Republicans and lobbyists, including interest groups aligned with the billionaire industrialists Charles and David Koch, who say the prospect of tax hikes could undermine future economic growth.

“I’d prefer not having it there. We’re probably going to have one. But I’d prefer not having it,” Republican Senate Finance Committee Chairman Orrin Hatch told reporters.

For more on Republican tax reform efforts, watch Fortune’s video:

‘Getting a Deal Done’

Republican Senator David Perdue, a businessman from Georgia, said lawmakers could find common ground on a measure that delays any tax hike for at least five years and spreads the prospective burden among those who benefit from Republican tax cuts.

Senator Rob Portman, an Ohio Republican on the tax-writing Senate Finance Committee, suggested such an approach may be gaining ground.

“It looks like the idea is part way through the first 10 years, there’d be an opportunity to see if the economic growth numbers are performing as expected. And if not, there would be a trigger mechanism over a 10-year period,” Portman said.

Democrats and independents were trying to persuade nonpartisan Senate officials to disqualify parts of the bill, including one to allow drilling in the Arctic National Wildlife Refuge, as impermissible under Senate rules, an aide said.

While some Republicans signaled determination to get the bill passed, they still did not have the votes.

“It’s time for us to saddle up and ride. And I’m ready to go,” Republican Senator John Kennedy of Louisiana told reporters.

Corker declined to say whether he would vote for the tax bill even if Senate Republican leaders agree to the kind of trigger mechanism he wants.

“I don’t do conjecture,” he told reporters, saying he could have other concerns about the final legislation. “There are also qualitative issues like the bill not getting any worse, that it doesn’t get more expensive.”