The bank props up U.S. exports by providing loans and credit insurance to foreign buyers to subsidize the purchase of American-made goods. For most of its 80-year history it has enjoyed ready bipartisan support. But in recent weeks extending the bank’s charter, which expires at the end of September, has emerged as a major skirmish in the corporatist-populist war within the Republicans party.

McCarthy had been a supporter of the bank in the past, voting as recently as 2012 to re-up it in a deal that Cantor engineered. But the blue-state Republican didn’t rocket to the top of House leadership with a tin ear for the politics of his conference. It was hardly lost on McCarthy that Cantor’s chumminess with the corporate lobby helped sink him. Or that some on the hard right panned his own promotion as another step in the wrong direction after the arguably more conservative Cantor got the boot.

So the McCarthy who showed up on Sunday appeared determined to demonstrate that he’s ready to channel the will of his rank-and-file, even if he’s not a fire-breather himself. It wasn’t just the Ex-Im bank. Challenged on his bona fides, McCarthy pointed out that he voted, twice, against the Wall Street bailout. He insisted the debate over comprehensive immigration reform, a top priority for the Chamber of Commerce crowd — not to mention the tech honchos McCarthy has assiduously cultivated — wait until the border is locked down. And he said he’ll oppose raising the gas tax to shore up the highway trust fund, another concern for corporate leaders worried by our crumbling infrastructure.

In the immediate term, the Ex-Im bank, an otherwise sleepy agency, will grab the bulk of the attention. That’s both because it’s prospects are so suddenly imperiled and also because it is a fight that seems to perfectly capture the animus dividing the GOP these days. Tea Party critics call the bank a classic example of the old-line Republican penchant toward crony capitalism, tapping taxpayer dollars to help mega-corporations like Boeing (BA) and Caterpillar (CAT) sell their wares abroad (and they got some fresh ammo today from a Wall Street Journal report detailing the suspension of four bank officials amid a probe of alleged kickbacks). The bank’s defenders note it returns a profit to the Treasury while enabling companies that grow jobs at home to keep pace with similarly-subsidized foreign competitors. In truth, the battle lines are not so neatly drawn: Delta Air Lines (DAL) has helped lead the opposition to the bank, CEO Richard Anderson recently acknowledged. That’s because the airline doesn’t want foreign carriers getting cheaper Boeing planes.

But Ex-Im’s boosters have evidently invested enough in the cause that McCarthy’s comments set off something approaching a panic among the top hired guns for big business in Washington. In a Monday afternoon conference call, U.S. Chamber of Commerce chief Tom Donohue warned that his group will turn up the heat on lawmakers by meeting them “back home where they live.” Talking up the lobby’s firepower, Donohue said, “I don’t know how this will all work out, but the Ex-Im bank will not fade quietly into the sunset. This is a serious deal, and it’s going to be dealt with that way.”

Donohue and National Association of Manufacturers president Jay Timmons, also on the call, projected certainty the bank would get a thumbs-up if brought to a vote on the House floor, but that only underscores the point. While House Republican leadership could likely reauthorize the bank by leaning on Democratic votes to muster a winning margin, McCarthy’s comments seemed to indicate he’s intent on keeping faith with his conservative flank. With a newly strengthened hand steering policy for the House GOP, he can deny the bank by denying a vote.

That said, it’s impossible to say this early on what’s in McCarthy’s head. Is this a signal to the rightwing he’ll be a reliable voice for them? After all, McCarthy, who is now poised to become the least experienced Speaker since the 19th Century, will have to stand for reelection to his post following the November elections, and he’ll need the pitchfork crowd’s support. Conversely, it could be a bid to buy some wiggle room with the right on higher-profile debates coming down the line, like immigration reform. Or a negotiating ploy with Senate Democrats designed to increase leverage as the bank’s expiration date swings into view. The fact that so many myriad theories are being floated is testament to how little the (not quite) four-termer is known. “The question is a good one: Is this leadership going to continue on this populist, anti-big business rant or is it going to recalibrate?” says Republican strategist John Feehery, formerly a top aide to House Republicans. “Cantor had been the pro-big business guy in the leadership, and I think Boehner is to a lesser extent. But obviously McCarthy, who’d previously been seen as someone who’d lend an ear to their cause — this might be a different path that he’s choosing.”

But one senior Democratic source in the House expressed skepticism that any breach between Republicans and the big business lobby could ever precipitate a realignment of interests, wherein business groups backed a Democratic candidate in a contested general election. A good test case could emerge soon: Mississippi voters are heading to the polls today to pick a Republican nominee for the Senate, with 36-year incumbent Thad Cochran trying to fend off a challenge from Tea Party favorite Charlie McDaniel. McDaniel appears to have Cochran on the ropes after forcing him into a runoff, and the Chamber has spent on ads touting the incumbent. But if McDaniel wins, would the Chamber similarly spend to help elect the Democrat nominee, former Rep. Travis Childers, who once won the Chamber’s Spirit of Enterprise award in recognition of his pro-business record? “I’ll believe it when I see it,” the Democratic source said.