U.S. President Donald Trump's administration held a Republicans-only briefing about U.S. strikes on alleged drug vessels near Venezuela, in what one senior Democrat on Thursday called a dangerous trend of increasing partisanship in national security.

"This is not how the system is supposed to work," Sen. Mark Warner of Virginia, ranking member and former chair of the Senate Intelligence Committee, told a news conference about the briefing, which took place on Wednesday.

"When you politicize decision-making about putting our servicemembers in harm's way, you make them less safe," he said.