A handful of lawmakers are saying President Barack Obama must get congressional authorization for military action in Iraq, a vote that could exacerbate tensions between the branches and present members with a difficult vote just before the midterm elections.

Mr. Obama's announcement of limited airstrikes last week aimed at slowing the advance of militants from the Islamic State toward the Kurdish city of Erbil initially triggered few complaints that he had usurped the power to declare war that Congress claims as its own.

But with the president warning over the weekend that "I don't think we're going to solve this problem in weeks," some lawmakers say what appeared to be a limited action is starting to look like the sort of sustained military engagement that requires congressional approval.

"Constitutionally, he should come forward with a plan to Congress and we vote for it or against it," said Sen. Rand Paul, R-Ky. "I have an open mind as to exactly what we do."

On Tuesday, Sen. Tim Kaine, D-Va., said lawmakers must authorize the action. And Rep. John Garamendi, D-Calif., said the president has a "responsibility of going to the American people and specifically Congress and laying out the reasons for past involvement and any future involvement."

"If you're sitting under the bomb that's coming down, you think it's an act of war," said Mr. Garamendi, whose district is home to two air bases with personnel engaged in the sort of surveillance and airdrops occurring in Iraq.

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