President Donald Trump threatened legal action over a Senate tradition Democrats have used to block certain judicial nominees, escalating a long-running dispute with Senate Judiciary Committee Chairman Chuck Grassley (R-IA).

The Judiciary Committee chair, and his fellow Republicans, have so far brushed off pressure from the president to nix the long-standing practice.

Senate Judiciary Committee Chair Chuck Grassley (R-Iowa) is pushing back on criticism from President Trump, who has railed against the “blue-slip” practice that allows home-state senators to veto nominees to district courts and U.