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.

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.

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