In the House, a Democrat and a Republican teamed up on Tuesday to introduce a resolution that would require congressional approval before U.S. troops could engage in offensive attacks against Iran. The measure by Representatives Ro Khanna, Democrat of California, and Thomas Massie, Republican of Kentucky, underscored a view held by many in Congress that Mr. Trump should not be able to decide on his own whether the United States wades deeper into the conflict. Thirteen additional Democrats signed on to the resolution, but no Republicans so far were supporting the effort.