WASHINGTON (AP) — President Donald Trump said Monday he won’t sign any other legislation into law until Congress passes a strict proof-of-citizenship voting bill that he says also must end Americans’ ability to vote by mail, a startling demand months before the midterm elections.

Trump told House Republicans during their annual retreat at his golf club in Florida that he doesn’t think they will win elections unless voting laws are toughened up to prevent fraud — even though mail ballots are popular in many states and federal law already requires that voters in national elections be U.S. citizens, with scant evidence that noncitizens ever try to vote.

The president wants to bolster the so-called SAVE America Act, which the House has already approved, and he pressed the Senate to push past its filibuster rules to send it to his desk. Voting experts have said the bill could disenfranchise some 20 million American voters who don’t have birth certificates or other documents readily available, a number that would likely swell with the additional ban on mail balloting that Trump is demanding.

“I’m not going to sign anything until this is approved,” Trump said, calling it his No. 1 priority.

“It’ll guarantee the midterms,” he said. “If you don’t get it, big trouble.”

The president’s determination to impose election changes has sounded alarms from voting rights groups as the Trump administration reaches deep into the realm of the states, which, under the Constitution, are in charge of election ballots and procedures in the U.S.

It also comes as his Republican Party, which narrowly controls Congress, faces headwinds this fall, its majorities at risk. Lawmakers have other priorities, including the more immediate need to fund the Department of Homeland Security as airport workers and others are going without paychecks amid the fight in Congress over the agency’s immigration and deportation operations.

Democrats largely oppose Trump’s efforts to seize more control over elections, and Senate Democratic leader Chuck Schumer said Trump’s demands would gridlock the chamber.

“This is what he does — he’s a thug, he’s a bully,” said Schumer of New York.

House Speaker Mike Johnson, who is close with Trump, appeared alongside the president on the stage with other GOP leaders applauding the bill.

But Senate Majority Leader John Thune has said using the so-called “talking filibuster” to pass the voting bill, as Trump and others propose, isn’t as easy as it seems.

“We can’t find a piece of legislation in history that’s been passed that way,” Thune told reporters.

Trump has said even if it takes six months, he wants the bill approved before any others will be signed into law.

The president continues to claim that he was not the loser in the 2020 election and his Justice Department is digging into his concerns. The FBI took the highly unusual move of seizing ballots and elections materials in Georgia and, most recently, in Arizona.

Trump wants the GOP-led Congress to build on the Safeguarding American Voter Eligibility, or SAVE America Act, with a new package, which he calls the “best of Trump.”

Already, the bill, as approved by the House, would require voters to present proof of citizenship with a passport or birth certificate when they register to vote. They would also have to show a photo ID when they cast ballots, as many states already require.

Trump would add one main provision: to ban mail-in ballots, which are used by many states nationwide. He would make exceptions for voters who are disabled, in the military, or in other situations.

A coalition of Trump supporters has been pushing versions of the SAVE America Act, with its proof of citizenship provisions a longtime goal of the president’s MAGA coalition. Trump also warned the House GOP that their existing version of the bill is inadequate. “We’re not going to sign a watered-down version,” he said.