Backlash mounting, President Donald Trump’s embattled Postmaster General Louis DeJoy will appear Aug. 21 before the Senate to testify on mail delivery delays and service changes that lawmakers and others are warning could imperil the November election.

Speaker Nancy Pelosi is calling the House back into session over the crisis at the U.S. Postal Service, setting up a political showdown amid growing concerns that the Trump White House is trying to undermine the agency ahead of the election.