Susan Davis

USA TODAY

WASHINGTON — A wary Congress voted Wednesday to authorize President Obama's mission to arm and train Syrian rebel forces as part of the administration's effort to dismantle the threat posed by the Islamic State militant group.

The bipartisan 273-156 vote came after days of debate in which lawmakers across the political spectrum expressed doubts about the scope and merits of the mission but conceded that the potential threat to the U.S. is too great to ignore.

"I will support any measure that will lead to the destruction of ISIS," said Homeland Security Chairman Michael McCaul, R-Texas. The group is also referred to as ISIL.

A majority of Democrats rallied around the president but also made clear that their support would not extend in the future to committing U.S. ground troops. "We (Democrats) are not there to support combat troops in any of those engagements," said House Minority Leader Nancy Pelosi, D-Calif., who voted for the resolution.

After the vote, Obama said in a statement, "Countries in the region and around the world are coming together to confront ISIL. The United States can make a decisive difference. Today's House vote is a step towards making that difference, and I urge the Senate to pass this bill without delay."

The resolution passed as an amendment to a stopgap spending bill that will sunset on Dec. 11, providing lawmakers a chance to reassess the mission and whether greater congressional authorization is warranted. The funding bill passed on a separate bipartisan 319-108 vote.

"I support what the president's doing, I'd like to take another look at it a couple of months from now and see how it's working out," said Senate Minority Leader Mitch McConnell, R-Ky.

The authorization is limited in scope to training up to 5,000 members of the Syrian opposition in Saudi Arabia. It provides no new funding and requires the administration to provide status reports to Congress. The Obama administration said the mission may be funded by international contributions, but the resolution authorizes the Pentagon to shift funds from other accounts if necessary.

Lawmakers expressed doubts about the ability to vet the Syrian rebel forces and warned that the arms provided to them could ultimately land in enemy hands. "We don't know if somehow down the line they will turn our guns right back on us," said Rep. Loretta Sanchez, D-Calif., a member of the House Armed Services Committee, who opposed the resolution.

Sanchez also said there was not enough of an international coalition behind a strategy that is still being formed. "I'd like to know who our coalition is, and what they're going to do before I vote for any plan," she said.

Armed Services Chairman Buck McKeon, R-Calif., who drafted the resolution, circulated a letter from former ambassadors Ryan Crocker and Robert Ford and retired generals Jack Keane and David Petraeus to build support.

"Building up the moderate opposition in Syria will be a key element of any successful strategy against ISIS. To be sure, after three years of war, it will take a long time to build the moderate opposition. But there is no viable alternative. The United States must set to this task immediately," the letter said.

The Senate is on track to approve the Syria authorization as part of the stopgap funding bill as early as Thursday. The legislation is the last major act of Congress ahead of the midterm elections.

While it is expected to pass, it also faces opposition in both parties. Sen. Rand Paul, R-Ky., a potential 2016 presidential candidate, opposes it. Sen. Joe Manchin, D-W.Va., announced his opposition on the Senate floor Wednesday.

"I strongly believe that if our military arms and trains Syrian rebels, we will be involving ourselves in a ground conflict that we cannot resolve where potentially everyone involved is our enemy," he said.