When Senate Republicans introduced their tax bill in mid-November, they faced competing interests: Some senators thought it wasn't generous enough for working-class families. Others thought it didn't deliver enough to business owners.

As Republicans moved closer to a final vote on the bill Friday night, they made several tweaks to the tax legislation. They announced more benefits for business owners, particularly wealthy ones, but they voted down a proposal by Sens. Marco Rubio (R-Fla.) and Mike Lee (R-Utah) to give low-income families a bigger tax break.

The disparate treatment underlined how the legislation — a massive rewrite of the individual and corporate tax code — has evolved since its first incarnation: What began as an effort that would favor wealthy individuals and corporations became, in many ways, even more tilted in their favor as the legislation made its way through the Senate.

Rubio and Lee had suggested paying for their idea by lowering the corporate tax rate from 35 percent to 21 percent instead of 20 percent.

“We could have helped so much more,” an exasperated Rubio had said earlier Friday, anticipating defeat. “With less than that one percent difference, we can make a huge difference in the lives of millions of Americans making between $20,000 and $50,000.”

An aide for Sen. Ron Wyden D-Ore.) carries a poster he used on the Senate floor to criticize the Republican tax bill Friday on Capitol Hill. (J. Scott Applewhite/AP)

That came after a series of other changes that took away from working-class and middle-class families benefits that had been in an earlier version of the bill.

When lawmakers needed a way to limit the legislation’s impact on the deficit to make it comply with Senate rules, they made the bill’s tax cuts affecting individuals temporary — ending in 2025 — while leaving in place ones that benefit corporations. The move would lead to a tax hike on many Americans in the middle of the next decade.

Likewise, when they needed to find additional ways to finance the corporate tax cut, leaders targeted the Affordable Care Act’s individual mandate for elimination. Such a move would lead 13 million to drop health insurance, including 5 million on Medicaid, according to the nonpartisan Congressional Budget Office.

At the same time, changes demanded by Sen. Ron Johnson (R-Wis.) to increase benefits for companies that pay their taxes through the individual tax code — a mechanism that experts say disproportionately benefits the wealthy — made it into the final version of the legislation released late Friday.

“It clearly makes inequality worse. The primary beneficiaries are the highest-income taxpayers,” said Adam Looney, a senior fellow in economic studies at the Brookings Institution who served as deputy assistant secretary for tax analysis in the Obama administration.

Republican leaders argue that providing deep tax cuts to corporations and wealthy business-owners will pump up the economy and deliver more jobs and higher wages to voters who, polls show, are deeply skeptical of the tax plan.

“In one bill, we’ve taken the U.S. from being one of the least attractive places to do business into one of the most attractive places to do business,” said Scott Hodge, president of the Tax Foundation, a think tank that has supported the bill.

Many independent studies agree the tax plan would trigger additional economic growth, but the question remains whether working-class Americans will ultimately reap additional benefits or whether most of the gains will go to the top.

“If this is our only major tax reform for another 30 years, then I think it’s a great disappointment,” said Alan Auerbach, a tax expert at the University of California at Berkeley who has co-authored research with the head of President Trump’s Council of Economic Advisers. Republicans “could have done much better,” said Auerbach. “Most of the benefits go to very high-income people.”

In interviews this week, Republican senators noted that the bill gives the middle class a direct tax cut, so it doesn’t matter what the rich receive as long as ordinary Americans are getting help.

“I’m not worried about the rich in this country. The rich generally take care of themselves. Out of a country of 300 million people, there aren’t that many really rich, rich people,” Sen. Richard C. Shelby (R-Ala.) said in an interview. “I do worry about the people who work every day that are paying more than their fair share.”

Republicans also point out they have made some changes that many liberals have advocated for years, such as scaling back the state and local tax deductions that are primarily used by upper middle class and wealthy taxpayers. But many GOP lawmakers argued it’s fair for the wealthy to get the biggest tax cut because they pay the most in taxes.

“It’s obvious that people who make money are going to pay more in taxes than people who don’t,” Sen. Johnny Isakson (R-Ga.) said in an interview.

Other Republicans argued that it was time for a change in direction.

“Income inequality increased dramatically under President Obama,” said Sen. Ted Cruz (R-Tex.). “High taxes, high regulations, and big government benefit the rich and hurt working men and women.”

According to the most recent analysis by the nonpartisan Tax Policy Center, the average taxpayer earning about $50,000 to $85,000 will get a tax cut of $850 in 2019. Meanwhile, the average taxpayer earning more than $1 million will get $34,130 in tax cuts.

The disparity grows even wider a decade down the road after the tax cuts for individuals expire.

By 2027, over half of taxpayers earning more than $500,000 a year get a tax cut of $500 or more in the Senate bill, according to Congress’s Joint Committee on Taxation. By contrast, just 5 percent of taxpayers earning $50,000 to $75,000 do.

President Trump has sold this bill as a win for all — a much-needed corporate tax reform and a cut for the middle class. But if helping the middle class was a core objective, there was a lot more than could have been done.

For example, the 2008 tax cut pushed by the Bush administration during the financial crisis delivered, on average, $1,010 to people earning $50,000 to $75,000, but people earning above $1 million got virtually no tax cut, according to the Tax Policy Center.

Auerbach says some of the pain for the middle class is not even clear in the bill, because Congress has to borrow at least $1 trillion to finance it — and that money one day may have to be paid back with spending cuts.

“Someone is going to have to pay for those deficits,” he said. “To the extent the deficits are addressed by cutbacks to entitlement programs, it could further exacerbate inequality.”

Some economists fear that the inequality created by the bill will deepen social divisions that have been on display across the United States and other Western countries in recent years.

“This [bill] is the reverse of what we need at a time of populist backlash against inequitable gains from globalization in advanced economies,” said economist Emmanuel Saez, a professor at the University of California at Berkeley and one of the leading experts on inequality.

Even among some Republicans who favor a deep tax cut, there was agreement that it should have gone further to support the working class.

“For Republicans, this is a once-in-a-lifetime opportunity to get corporate tax reform done. It will help growth, but there could have been more done for the lowest-income households,” said Aparna Mathur, an economist and scholar at the right-leaning American Enterprise Institute.

Jeff Stein and Andrew Van Dam contributed to this report.