The Trump administration lifted sanctions on a Venezuelan general who broke ranks with President Nicolás Maduro’s regime in an effort to encourage others to do the same, and warned Venezuela’s top judges of consequences if they don’t back opposition leader Juan Guaidó.

Vice President Mike Pence’s speech Tuesday announcing the actions was the first major address from the Trump administration since the unraveling last week of a Venezuelan opposition plan to remove Mr. Maduro from power. The failure of that deal provoked street...