After threatening to vote "no" on the GOP tax bill, Sen. Marco Rubio (R-Fla.) and Sen. Bob Corker (R-Tenn.) pledged their support when the bill was finalized. (Jenny Starrs/The Washington Post)

President Trump, Sen. Bob Corker (R-Tenn.) and other members of Congress with expansive real estate holdings were already primed to benefit from the tax overhaul bill nearing approval.

Late last week, things got even better.

On Friday, lawmakers added a provision to the tax package offering a 20 percent deduction for income earned from “pass-through” entities — companies that don’t pay corporate taxes but pass through the income to be taxed as part of the owner’s personal tax bill.

“A lot of commercial real estate entities are structured as pass-throughs, so clearly the provision by and large would benefit those kind of enterprises,” said Joseph Cordes, a George Washington University economics professor and former Treasury Department official.

Disclosure of the new provision quickly put Corker, a former construction executive who had initially opposed the bill before signaling his support, on the defensive. Some critics pointed to the timing of Corker’s change of heart, coming on the same day the provision had been added. The hashtag #CorkerKickback quickly began trending on ­Twitter.

Corker denied any involvement in the change. After having initial reservations about how the overall bill would drive the nation’s debt higher, he said he now believes that the legislation marks a “once-in-a-generation opportunity.”

The provision in question was added as House and Senate leaders tried to reconcile their respective plans to change the tax system. GOP leaders initially designed the tax overhaul to benefit companies that employ a substantial number of workers. But the changes added to the bill Friday would provide huge tax breaks to companies that typically have few or no employees — benefiting business owners including Trump, Corker and others.

“This last addition on Friday night is the biggest jackpot for Donald Trump yet,” said Steve Rosenthal, a senior fellow at the Urban-Brookings Tax Policy Center at the Urban Institute.

Ed Kleinbard, a former chief of staff of Congress’s Joint Committee on Taxation and now a law professor at the University of Southern California, called it a “complete giveaway with a discounted tax rate” to real estate partnerships and investors.

The social media backlash prompted Corker, who is retiring at the end of next year, to issue a statement saying he “had no involvement in crafting” the legislation and had made no request that the specific provision be added.

He wrote a letter to Sen. Orrin G. Hatch (R-Utah), vice chairman of the conference committee finalizing the bill, asking how the provision was inserted, then shared his letter with reporters.

Hatch said Monday morning that it was he, not Corker, who added the provision, writing to Nashville’s Tennessean newspaper that he was “unaware of any attempt by you or your staff to contact anyone on the conference committee regarding this provision or any related policy matter.”

Hatch also defended the provision, saying it combined elements of the House and Senate versions of the bill and provided fairness between the breaks that other corporations would receive with those for pass-through companies. In its version, the House tried to tailor lower rates to companies that employ substantial numbers of employees by excluding independent operators such as lawyers, lobbyists and accountants. With the new provision, Republicans ditched that effort, allowing lower rates for all pass-through firms, regardless of the likelihood of it boosting job creation.

“For more than a year, ­tax-writers in the House and Senate have worked to craft legislation that not only provided relief for ‘C’ corporations but also delivered equitable treatment for pass-through businesses at a similar level,” he wrote.

Trump has defended the Republican effort to overhaul the nation’s tax code, saying it would make him a “big loser” and instead benefit the middle class.

But nearly all of the more than 500 companies listed in Trump’s past financial disclosures, including the Trump Organization, are structured as pass-through entities. And the savings for Trump could be huge: His 2005 tax return showed he had more than $109 million in income from businesses, partnerships and pass-through entities.

Even before the pass-through deduction was added, many commercial real estate investors were celebrating the tax changes. ­Revathi Greenwood, a research executive at services firm Cushman & Wakefield, said “commercial real estate is a winner” late last week.

Ryan Severino, chief economist at real estate service firm JLL, said the 20 percent deduction was an additional benefit because “pass-throughs are a very popular form of [real estate] ownership. This deduction will increase after-tax profit.”

Cordes, who oversaw the same section of the tax code during 1986 tax retooling under President Ronald Reagan, said it was “inconceivable” that Trump and other commercial real estate investors wouldn’t benefit financially from the proposed tax changes.

He said under Reagan, lawmakers moved away from incentivizing similar, often passive, investments.

“There was a great concern at that time that we were creating too much incentive to invest in commercial real estate rather than research and development and other things,” he said.

Kleinbard disputed the industry’s messaging that the deduction, like other tax changes, would help create jobs.

“A real estate developer typically has very lean staff: They lease out the buildings, they contract out the routine service so those people are not their employees,” he said.

Mike DeBonis and Damian Paletta contributed to this report.