U.S. Senate Judiciary Committee Chair Chuck Grassley said on Wednesday he was “offended” and “disappointed” by President Donald Trump’s social media posts targeting him for refusing to end a custom that allows Democratic senators to effectively veto new nominees to serve as judges and prosecutors in their states.

At the start of a Senate Judiciary hearing on four of Trump’s judicial nominees, Grassley, an Iowa Republican, took issue with the president’s call late Tuesday on his social media platform Truth Social for an end to the so-called “blue slip” process in the Republican-led Senate.

Senators by custom must return blue slips, named for the color of the form, in order for any district court or U.S. attorney nominees from their states to advance and receive a hearing before the committee.

Trump in a post on Tuesday called on Grassley to have the “COURAGE” to end “hoax” and “scam” blue slips, which he said are allowing Senate Democrats to “have an ironclad stoppage of Great Republican Candidates” to serve as judges and U.S. attorneys.

Trump then early Wednesday reposted messages from Truth Social users focused on the 91-year-old senator’s age and encouraging him to comply with Trump’s wishes.

“I was offended by what the president said, and I’m disappointed that it would result in personal insults,” Grassley said.

The custom has allowed senators in both parties to block nominees they opposed in their home states and ensure the White House consults with them to find acceptable picks.

Senator Dick Durbin, the committee’s top Democrat, during Democratic President Joe Biden’s tenure resisted calls by progressive advocates to do away with blue slips when he chaired the panel.

He thanked Grassley for likewise standing by the custom. “I hope it continues to be the case,” he said. Grassley responded: “Yes.”

Trump’s tirade came after New Jersey U.S. Senators Cory Booker and Andy Kim, both Democrats, effectively blocked the nomination of Alina Habba, the president’s former personal lawyer, to serve as their state’s top federal prosecutor by refusing to return blue slips.

After judges in New Jersey also declined to appoint her to the position of U.S. attorney, the Trump administration withdrew her nomination and pursued a new maneuver to keep her in the job in an acting capacity that included firing the prosecutor whom a federal court had tapped to replace her.

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(Reporting by Nate Raymond in Boston; Editing by David Bario and Marguerita Choy)