WASHINGTON — Fresh from victory in the midterm elections, congressional Republicans thought President Barack Obama might be chastened.

“What did the president do? He pulled the pin on the grenade two weeks after the election,” said Rep. Pat Tiberi, R-Ohio, a close ally of House Speaker John Boehner. “I don’t think anybody knows or can predict what happens and the carnage that this creates quite frankly for the legislative process.”

But Republicans agree Obama’s immigration plan must be stopped.

“It is our obligation and responsibility to fight this brazen power grab that doesn’t solve the real problems,” House Majority Leader Kevin McCarthy, R-Calif., said following the president’s announcement of an executive order to shield as many as 5 million immigrants here illegally from deportation, and grant them work permits.

“Our Constitution does not grant the president the authority to legalize millions of immigrants with the stroke of a pen.”

Obama’s announcement presented party leaders with a dilemma: How to undo an action set to take effect without Congress doing anything, with no obvious legislative vehicle for doing so and Obama able to veto any legislative solution they derive.

Conservative lawmakers are pushing to insert language in upcoming must-pass spending bills to block Obama’s order. Party leaders warn that could lead to a government shutdown.

“They’re contriving red herring arguments to get to the point where enough members will walk out of this Congress and go home for Thanksgiving and say, ‘Well, there’s nothing we can do,’” said Rep. Steve King, R-Iowa. “I feel sorry for them if they step up in front of their constituents and say ‘Congress can’t do anything. We have to let the president violate the Constitution.’”