WASHINGTON — Senate critics of President Barack Obama's war on terror efforts are warning the White House must come to Congress for authority if the president wants to launch significant military action in Iraq.

Democrats and Republicans alike have raised questions about the authority of the Obama administration to wage war against terrorist groups, the continued territorial gains by ISIS (the Islamic State in Iraq and Syria) and deteriorating situation in Iraq have given the debate new urgency on Capitol Hill. The administration announced Monday they would dispatch up to 275 U.S. troops to protect the U.S. Embassy in Iraq.

"A new war has started and if people want to go be involved in a new war, the job of Congress is to vote on it," Republican Sen. Rand Paul said Tuesday. "I don't think you can have a Congress of 10 years ago make a decision for the people here 10 years later."

"I think the president has essentially admitted the Iraq AUMF has functionally expired," said Democratic Sen. Chris Murphy, who, along with Paul, is part of a bipartisan group of lawmakers who have pushed to reign in the administration's authority under the 2001 Authorized Use of Military Force resolution. "I think we have over a dozen AUMFs on the books and we need a comprehensive look at which are functional and which are obsolete. The Iraq AUMF is functionally obsolete."

"If he's looking for a longer-term military engagement I don't think he can do that under the Iraq AUMF … he's got to come back to Congress," Murphy added.

The question of whether Obama can launch military operations against ISIS under existing legal authority remains an open one. In theory, he could invoke Article II of the Constitution, as he did in launching air strikes against Libya in 2011. But that decision caused a firestorm of criticism in Congress, and the administration could face significant bipartisan backlash.

Alternatively, the administration could invoke the 2001 Authorized Use of Military Force resolution, which has been used in the increased use of drones. But because al-Qaeda has broken with ISIS, that could prove difficult.

Likewise, while parts of the 2003 Iraq War resolution appear to give the administration broad authority to conduct military operations in the country, legal experts are split on whether it remains operable or if the technical end of the war means the administration would need a new resolution.

Regardless of what authority the White House ends up invoking, Democratic allies in the Senate made clear Tuesday they don't want to see any military action.

"Nothing's changed," Sen. Jon Tester of Montana said. "If any one is surprised by what's happening in Iraq they certainly saw the world from a different view than I saw it. Get our troops home, get our people out of there, they've been fighting for 2,000 years, we aren't going to stop them."

Asked if he felt Obama should come to Congress for authorization of any expanded military activity in Iraq, Tester said simply, "It'd be great if he would."