President Donald Trump pushed Sen. Chuck Grassley (R-IA) on Tuesday to toss a Senate tradition that has empowered Democratic senators to unilaterally block the president’s judicial nominees.

Grassley chairs the Senate Judiciary Committee, which oversees judicial nominations. The “blue slip” custom on the committee is not required, but was adopted as an internal vetting procedure to encourage communication between the White House and the senators of the state in which the nominee will serve, giving senators influence over appointments in their states.

Democrats have stalled Trump’s nominees by refusing to give their assent with “blue slips,” a blue-colored form given to senators where a federal judicial nominee would serve. If the senator withholds or returns a negative blue slip expressing disapproval, they can use the custom as a tool for obstruction. The tradition’s enforcement is controlled by the chair’s discretion.

“Chuck Grassley, who I got re-elected to the U.S. Senate when he was down, by a lot, in the Great State of Iowa, could solve the ‘Blue Slip’ problem we are having with respect to the appointment of Highly Qualified Judges and U.S. Attorneys, with a mere flick of the pen,” said Trump. “Democrats like Schumer, Warner, Kaine, Booker, Schiff, and others, SLEAZEBAGS ALL, have an ironclad stoppage of Great Republican Candidates.”

“Put simply, the President of the United States will never be permitted to appoint the person of his choice because of an ancient, and probably Unconstitutional, ‘CUSTOM,’ that if you have, even one person in the opposite Party serving in the U.S. Senate, he/she must give consent, thereby completely stopping the opposite Party’s Nomination,” he added.

The president said that in states with Democratic senators, his own judicial nominees would have to either be a Democrat or “a weak and ineffective Republican” to receive blue slip approvals.

“I would never be able to appoint Great Judges or U.S. Attorneys in California, New York, New Jersey, Illinois, Virginia, and other places, where there is, coincidentally, the highest level of crime and corruption — The places where fantastic people are most needed!” the president said.

Trump said that former President Joe Biden broke the blue slip custom at least twice during his term, and that previous presidents have also worked around the Senate tradition.

A Grassley spokesman suggested in a statement on Tuesday that, despite the president’s pressure, the Judiciary Committee chair would retain the blue slip custom.

“Chairman Grassley has already successfully moved U.S. Attorneys through committee who have received blue slips from Democrats, including Senators Warner and Kaine of Virginia and Klobuchar and Smith of Minnesota,” the spokesman said, according to Politico. “When a nominee comes out of committee all 100 senators have a say on the nomination and part of their consideration is based on the home state senators’ input.”