CARACAS, Venezuela — Venezuela plunged deeper into turmoil Monday as security forces put down a pre-dawn uprising by national guardsmen that triggered violent street protests, and the Supreme Court moved to undercut the opposition-controlled congress’ defiant new leadership. Socialist party chief Diosdado Cabello said 27 guardsmen were arrested and more could be detained as the investigation unfolds. The mutiny struck at a time when opposition leaders have regained momentum in their efforts to oust President Nicolas Maduro.