President Trump is escalating his criticism of Senate Judiciary Committee Chair Chuck Grassley (R-Iowa) for his unwillingness to overhaul the “blue slip,” a move that has further dismayed Senate Republicans.

Senators approve of a nominee by returning their blue slip to the Judiciary Committee Chairman. If a senator does not return their blue slip or returns it with objections, the nominee does not advance. In blue states like New York, some of Trump's judicial nominees have stalled out because Democratic senators have not returned blue slips.

Senators are fiercely protective of the longstanding precedent that gives them deference over who serves as U.S. attorneys and district court judges back home.