Yesterday, the U.S. House passed a sweeping tax bill, but it’s not clear how much it will do to help small businesses, which create the majority of jobs in the country.

At issue is a proposed 25% tax rate for so-called “pass-through” businesses–such as partnerships, S-corporations (publicly held corporations that elect to be taxed as partnerships) and limited liability companies (LLCs). Unlike traditional C-corporations, their income is not subject to corporate income tax; instead, their owners pay taxes on their share of the business’ profits at their personal tax rates, which currently top out at 39.6 percent for the highest-income individuals.  (The House bill passed yesterday leaves the 39.6 percent rate in place for millionaires.)

The Senate version, which passed the Senate Finance Committee yesterday,  takes a different approach from the House by creating a new 17.4% deduction for pass-through businesses. The deduction is limited to 50% of the taxpayer’s allocable share of W-2 wages. Under a special rule, the W-2 wage limit does not apply in the case of taxpayers with taxable income not exceeding $500,000 for married individuals filing jointly or $250,000 for other individuals. (The benefit of the deduction for service businesses is phased out over the next $100,000 of taxable income for married individuals filing jointly or $50,000 for other individuals.)

But trouble is brewing in the Senate.  Sen. Ron Johnson, Republican from Wisconsin, said Wednesday he is opposed to both the House and Senate bills as it relates to small business.  Johnson said both bills favored corporations over small businesses and pass-through entities.  (Both the House and Senate versions would drop the corporate rate from 35% to 20%.)

It’s unclear how this will all shake out.  The full Senate won’t begin debate on its tax plan until the week after Thanksgiving and whatever comes out of the Senate–which may or may not happen–would have to be reconciled with the House bill in a conference committee.

One thing is clear:  The House version would be a windfall for timber companies, real estate developers, private equity firms, hedge funds and other types of large businesses. In other words, the donor class.

The Tax Policy Center’s Steven M. Rosenthal said that under the House plan, most small-business owners will not even benefit from the proposed 25% tax rate because they don’t earn enough income.  He notes that nearly 90% of pass-through owners already pay a tax rate of 25% or less under current law.

So, who would benefit then? According to a Nov. 8 post by Rosenthal on TaxVox, “the ones who could benefit most from the 25% rate are those in the 39.6% bracket, who currently receive half of all pass-through income.”

During the 2016 presidential campaign, then-GOP presidential nominee Donald Trump actually introduced a proposal that would have dropped the tax rate on pass-through entities to a mere 15%, which critics dubbed the “Trump loophole.”

Through the Trump Organization, Trump owns more than 500 pass-through business entities, mostly LLCs.  The House proposal would slash the tax rate on profits from these entities by more than a third.

But we don’t have a clear view of just how big a windfall that would confer on Trump because he has refused to release his tax returns–but it is potentially millions of dollars. Trump’s family members, including Ivanka Trump and husband Jared Kushner, also have pass-through businesses, and stand to reap a windfall if the House plan’s tax treatment of pass-through entities ever becomes law.