Charles Krauthammer is probably America’s most influential conservative pundit, and a convenient barometer of the Republican Party’s temperament at any given moment, so it’s worth sitting up and taking notice when he says President Obama is on the cusp of committing “an impeachable offense.”

We should sit up not because what he’s saying about Obama’s plan to protect millions of unauthorized immigrants with deep roots in the U.S. from deportation is accurate. But because it gives you a clearer sense of the incredible pressures Republican leaders will face in the coming weeks. It’s a reminder that despite all the election-season jitters Obama’s proposal created in the Senate Democratic caucus, the specter of executive action has always spooked Republicans more than Democrats.

When incoming Senate Majority Leader Mitch McConnell said unilateral immigration measures would be tantamount to waving a red flag in front of a bull, he wasn’t just playing an expectations game. He was accurately describing the volatility of the right wing of the GOP. A group of over 50 Republicans have asked House appropriators to defund Obama’s proposal. If they ratchet up their demands by refusing to support any government funding plan that doesn’t tie Obama’s hands, Republicans will lose significant leverage in negotiations over the year-long spending plan. On the other hand, if Republican leaders heed their advice, they’ll be teeing up another government shutdown fight.

GOP leaders obviously don’t want another shutdown. McConnell has all but taken a solemn oath not to allow Republicans to commit another unforced error like that. But House Speaker John Boehner can’t just tell these guys to pound sand. Which is why he told reporters Thursday that while his goal is “not to shut down the government,” he’s leaving “all options…on the table” to stop Obama from “violating his own oath.”

There are three tools Republicans can use to stop Obama, but toxic Republican politics preclude the only one—a pledge to vote on comprehensive reform—that would actually work. That leaves the spending and impeachment powers. If, like Boehner, Republican hardliners truly believe the president is preparing to violate his oath of office, and an appropriations fight won’t stop him, then suddenly Krauthammer’s option becomes the last arrow in their quiver.