Republicans voted to reject the measure, as Democrats pressed Congress to take a stronger role in Trump's high-stakes campaign against Venezuelan President Nicolás Maduro.
Lawmakers, including top Republicans, have demanded that the Trump administration provide them with more information on the US military strikes against alleged drug-smuggling vessels in the Caribbean Sea and eastern Pacific Ocean.
However the vote on legislation that would essentially forestall an attack on Venezuelan soil by first requiring congressional authorisation, showed the extent of GOP senators' willingness to allow the Trump administration to continue its buildup of naval forces in the region.
The legislation failed 49-51, with Senators Rand Paul and Lisa Murkowski the only Republicans voting in favour.
US naval forces are building an unusually large force, including its most advanced aircraft carrier, in the Caribbean Sea, leading many to the conclusion that Trump's intentions go beyond just intercepting cocaine-running boats.
"It's really an open secret that this is much more about potential regime change," said Democrat Senator Adam Schiff, who pushed the resolution. "If that's where the administration is headed, if that's what we're risking — involvement in a war — then Congress needs to be heard on this."
At a hearing in the Senate Armed Services Committee earlier Thursday, Senator Roger Wicker, the Republican chair, said that many senators have "serious concerns about the Pentagon's policy office" and that Congress was not being consulted on recent actions like putting a pause on Ukraine security assistance, reducing the number of US troops in Romania and the formulation of the National Defence Strategy.
As pushback has mounted on Capitol Hill, the Trump administration has stepped up its briefings on the campaign in the Caribbean, including sending both Secretary of State Marco Rubio and Defence Secretary Pete Hegseth to a classified briefing Wednesday for congressional leaders on the strikes against vessels.
The officials gave details on the intelligence that is used to target the boats and allowed senators to review the legal rationale for the attacks, but did not discuss whether they would launch an attack directly against Venezuela.
Many GOP senators expressed support for Trump's campaign, which has killed at least 66 people in 16 known strikes.
Trump ally Senator Lindsey Graham, argued that the War Powers Act gave lawmakers too much power over military decisions and that Congress has other means to check the president's decisions.
"I like the idea that our commander-in-chief is telling narco-terrorist organisations you're not only a foreign terrorist organisation, but when you engage in threats to our country — a boat headed to America full of drugs — we're going to take you out," Graham said.
However, Republican Senator Todd Young, said while he'd voted against the legislation he was "troubled by many aspects and assumptions of this operation and believe it is at odds with the majority of Americans who want the US military less entangled in international conflicts."
Democrats say the Trump administration is using a flimsy legal defence for an expansive military campaign that is putting US troops and the nation's reputation at risk.
Senator Jack Reed, the top Democrat on the Senate Armed Services, charged that Trump is engaging in "violence without a strategic objective" while failing to take actions that would actually address fentanyl smuggling.
"You cannot bomb your way out of a drug crisis," he said.
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