Dozens of Republican attorneys general may prove a powerful check on the next president.

Most Americans won’t have heard of Luther Strange, though that might be about to change. Next week the Alabaman ascends to the top of what by that point could be one of the most consequential GOP organizations in the country. That would be the Republican Attorneys General Association, the umbrella group for the states’ conservative prosecutors—and a new force to reckon with in American politics. Attorney general races don’t get much national attention, but these days they should. Under a Hillary Clinton presidency in particular, Republican AGs may prove the most effective check on both an overweening federal government and growing abuses by liberal prosecutors. “Health care, immigration, climate regulations—the AGs are acting as a last line of defense, but also in an agenda-setting capacity,” Mr. Strange told me at a recent meeting in Washington, D.C. “And we’ll be in an even stronger position to do this after Election Day.” His words are a nod to the extraordinary transformation Republican AGs have undergone in the era of Barack Obama. Not many years ago, those AGs had little to do with each other and were focused on policing occasional state crime. But the combination of the president’s growing federal overreach, and a new generation of activist, conservative law dogs, has inspired a powerful and cohesive new AG movement.

Republicans currently hold 27 AG seats, and they are likely to emerge from Tuesday with more.

In North Carolina, state Sen. Buck Newton is in a tight race against Democrat Josh Stein, in a contest that may hinge on the upticket re-election fortunes of Donald Trump and Gov. Pat McCrory. Republicans are also feeling more confident they’ll hold on to West Virginia, where rebel AG Patrick Morrisey.

They’ll need that strength, particularly under a Clinton presidency. With Republicans near certain to hold the House, and potentially the Senate, Mrs. Clinton will undoubtedly build on Mr. Obama’s extralegal habit of ruling via executive order or regulation. The GOP AGs will be the primary way for conservatives to challenge those edicts, in court. Under a Trump presidency, they will be an invaluable tool in dismantling some of the Obama federal behemoth. That job gets tougher, obviously, if Mrs. Clinton gets to pick a Supreme Court justice to replace Antonin Scalia, as well as to pack appeals courts with liberal nominees. A liberal judiciary likely robs the country of any legal recourse against lawless federal governance.

A growing Republican AG force will also prove crucial in parrying a new era of liberal prosecutorial intimidation. Liberal state AGs are moving ever more toward bogus investigations and hardball tactics designed to strangle corporations and conservatives into settlements or silence. Mr. Strange has himself most recently been leading a coalition of colleagues in pushing back against a group of liberal AGs engaged in a witch hunt against Exxon Mobil and conservative think tanks over climate science. Trump or Clinton, we still don’t know. What we do know is that an army of Republican legal fighters is standing by, ready to ride herd on the next Oval Office.

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