Liberal groups demanded the resignation of a top House Democrat on Thursday after he was caught on a secret recording trying to strong-arm a progressive candidate to nix his congressional campaign and clear the way for party leaders’ preferred pick to win. Rep. Steny H. Hoyer, the second-ranking Democrat in the House, told Levi Tillemann, a Democrat running in Colorado’s 6th Congressional District, to drop out because “a judgment was made very early on” that opposing candidate Jason Crow, an Army veteran, was the party’s choice to take on a vulnerable Republican. The recording, which Mr. Tillemann released to the...