THE 2020 presidential election culminated in the harrowing Jan. 6 attack on the Capitol by rioters stirred up by the losing candidate, then-President Donald Trump. In recent days, lawmakers in both chambers of Congress have responded by pushing for accountability (a bipartisan independent commission to investigate the insurrection), prevention (beefed-up security) and structural change (the H.R. 1 voting access and campaign reform bill).

What’s been missing so far is a rewrite of the arcane and outmoded law that helped set the stage for much Republican mischief on Jan. 6: the Electoral Count Act of 1887, enacted to prevent a repeat of the struggle over dueling state slates of ostensibly certified presidential electors that paralyzed the 1876-1877 election — and has not substantially changed since then.

It’s Congress’s job to count the electoral votes and certify the presidential election winner. This should be a pro forma exercise, but pro-Trump Republicans led by Sen. Josh Hawley (Mo.) weaponized the Electoral Count Act to disrupt it. Specifically, Mr. Hawley et al. exploited open-ended language that allows Congress to reject electoral votes “not regularly given,” arguing that certain state outcomes could have been marred by fraud — per Mr. Trump’s ludicrous claim that he, not President Biden, had actually won. Mr. Hawley said he was merely trying to assure that these phony allegations were fully aired. In reality, his maneuver could have led to a virtual coup d’etat — and, at a minimum, constituted an attempted usurpation of state power by Congress. By enabling a partisan majority of Congress to overturn a presidential election, Mr. Hawley’s challenge could have sent U.S. democracy into a “death spiral,” as then-Senate Majority Leader Mitch McConnell (R-Ky.) put it.

Fortunately, bipartisan majorities in both chambers rejected it, albeit with a disturbingly large minority of Republicans in support. Yet the underlying statute remains, like an unexploded bomb ready to detonate in some other year — perhaps as soon as 2024. The spirit behind the failed effort to overturn the 2020 result is far from banished, as the GOP moves to alter state election laws around the country — including restrictive voting rules and one proposal, in Arizona, to put the legislature in charge of certifying election results, rather than the secretary of state.

Congress should move now, well before the next presidential campaign, to make it crystal clear that the states, not Congress, are the ultimate arbiters of their elections for presidential electors, and that their votes, once certified, will ordinarily be presumed “regular.” The law should also be changed to require significantly more than a single member of each chamber to initiate a challenge — the minimum under current law. This could help deter frivolous or bad-faith efforts such as Mr. Hawley’s. The president pro tem of the Senate should handle the actual vote count to eliminate any notion that the vice president could purport to decide the votes’ validity himself as presiding officer — a notion Mr. Trump disgracefully invoked to pressure his own vice president, Mike Pence.

Given the majorities that rejected Mr. Hawley’s bid in January, it is just barely possible that bipartisan consensus could be forged to achieve these limited but vital reforms. Without them, the ambitious agenda to protect democracy against another Jan. 6 remains incomplete.

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