Updated on November 15 at 4:13 p.m. ET

President Trump and congressional Republicans have repeatedly insisted that the top priority of their tax reform is delivering relief to the middle class. But under a significant change to the Senate’s plan announced late Tuesday night, that relief for most people will now only be temporary, and millions of middle-class families could actually see a tax increase in 2026 if Congress doesn’t act again.

As I recently reported, the competing Republican tax bills were both over-budget, forcing party leaders to scale them back if they hoped to pass legislation under Senate rules without Democratic votes. They essentially had two choices: They could slap an expiration date on the proposal’s large corporate tax cut—from 35 percent down to 20 percent—or they could sunset the provisions benefitting individuals.

For now, Republicans are siding with businesses, keeping the lower corporate rate permanent while setting nearly all of the individual tax cuts to expire in eight years, at the end of 2025. The decision is a nod to conservative economists who argue that permanence in business tax rates is key to producing desired growth in the GDP, because companies are more likely to plan expansion and investments years ahead of time. And it’s also a bet that future Congresses—whether under Democratic or Republican majorities—will extend the cuts for individuals to stave off a politically unpopular tax increase.

Yet the choice dents the GOP’s message that the bill is targeted chiefly at middle-class families and not big business. “Bottom line, my colleagues on the other side have shown their hand,” said Senator Ron Wyden of Oregon, the top Democrat on the Finance Committee, which wrote the bill and held a combative markup of the revised proposal on Wednesday less than 12 hours after the changes were unveiled. Republicans on the panel hope to approve the bill this week so the full Senate can vote on it after Thanksgiving. The House is set to pass its version of the tax bill on Thursday, and party leaders want to reconcile the legislation and send it to Trump’s desk by Christmas. Adding to the GOP’s hurry is the Senate special election next month in Alabama: If Democrat Doug Jones defeats the scandal-plagued Roy Moore, the Republican majority come January would be down to a single seat.

Wyden said the changes ordered by Chairman Orrin Hatch of Utah created a “double standard” in which handouts for corporations were “etched in stone” while relief for families would go away. And because Republicans are making permanent changes to the way inflation is calculated in tax policy, many people would see a net tax increase from what they pay today once the personal tax cuts expire. “For middle-class families, the deal looks worse and worse,” Wyden said.

In the short term, middle-class families should do better under the revised Senate bill than the original. Hatch slightly lowered individual income rates and increased the child tax credit to $2,000. (The credit is currently $1,000 per child, and the first Senate draft would have bumped it up to $1,650.) But like the rest of the individual provisions, including a repeal of the alternative-minimum tax and the doubling of the estate-tax exemption, those perks would go away in eight years.

Republicans readily acknowledged they only sunset the personal tax cuts to abide by Senate budget rules, which forbid the tax legislation from adding to the deficit after the first decade. They would need 60 votes, including at least eight from Democrats, to get around that. “We can make the individual side permanent,” Senator John Thune of South Dakota said. “All it takes is a few Democrats to help us do that.”

Democrats, of course, are in no mood to assist Republicans in passing a bill they consider fiscally irresponsible and skewed toward the rich. They spent much of Wednesday’s hearing hammering the GOP for inserting a repeal of the Affordable Care Act’s individual mandate into the bill, a move that helped them offset some of the tax cuts in the budget. While Republicans argued they were eliminating a penalty that hits lower-income Americans disproportionately, Democrats countered that scrapping the penalty would actually raise costs for most people through higher insurance premiums—a view shared by the nonpartisan Congressional Budget Office. “You are spending $338 billion to make tax cuts for corporations permanent,” Democratic Senator Claire McCaskill of Missouri said.

Republicans have downplayed the impact of sunsetting the individual tax cuts, offering assurances that lawmakers in the future won’t allow them to go back up, at least not for the middle class. They have recent history on their side. Under President George W. Bush, Republican majorities enacted temporary tax cuts to abide by Senate rules. A decade later, Democrats extended all of them for two years under former President Barack Obama, and then in early 2013, Obama struck a deal with Republicans to make permanent all of the cuts except those on income over $400,000.

“I think that’s a fight we can win,” said Jason Pye, director of public policy and legislative affairs for FreedomWorks, the conservative advocacy group. He told me he would have preferred to see all of the tax cuts made permanent but that he understood the constraints Republicans were under. “I don’t care for it, but I’ll live with it,” he said. “There are certain concessions that we have to make and that conservatives have to make.”

The GOP bill ran into its first sign of trouble on Wednesday afternoon when Senator Ron Johnson of Wisconsin told the Wall Street Journal that he would oppose it as written. Johnson complained that the bill’s business tax cuts were too skewed in favor of corporations as opposed to smaller firms and “pass-through” entities. “If they can pass it without me, let them,” Johnson told the newspaper. “I’m not going to vote for this tax package.”

So far, he’s the only Republican senator planning to vote no, and the party can afford only one more defection if he doesn’t change his mind. But making so many of the provisions temporary while insisting they’ll never go away risks support from deficit hawks like Senators Bob Corker of Tennessee and Jeff Flake of Arizona, since the change obscures the true cost of long-term tax cuts. “We can’t cut, cut, cut today and assume Congress will grow a backbone later,” Flake said earlier this month.

But the assumption inherent in the GOP’s argument is that Congress won’t ever grow that backbone. In essence, by relying on future Congresses to extend the tax cuts they’re enacting now, Republicans are applying the lessons they learned the hard way in their struggle to repeal Obamacare: Once a benefit makes it into law, it’s nearly impossible for lawmakers to take it away.