Violent threats against lawmakers have Congress on edge

Rep. G.K. Butterfield was proud to be in Congress. Some years ago, the veteran Democrat installed a vanity message on his congressional license plate, broadcasting the district he represents: North Carolina 1.

Those days are over.

In recent years, the number of menacing threats against sitting members of Congress has ballooned, forcing the Capitol Police to launch thousands of investigations; prompting a flood of new funding for lawmaker security back home and in Washington; and impelling lawmakers to take remarkable precautions to ensure they don’t become the next target of...