The Electoral College gambit won’t work this week because House Democrats won’t go along, but imagine if Republicans ran the House and did. Eighty-one million Americans who voted for Mr. Biden would be disenfranchised by an insider scheme. The political response would be volcanic, and understandably so. Republicans would be crushed in the 2022 midterms, and Mr. Trump would promptly be impeached again. More Senate Republicans might vote to convict.

In our view this week’s exercise is also unconstitutional. The text of the original charter, elaborated by the 12th Amendment, gives state legislatures the power to appoint electors. The Vice President is charged to open the votes to be counted—nothing more.

The Electoral Count Act of 1887, which the House and Senate will act upon, is unconstitutional in giving Congress the ability to second-guess those state decisions. In stretching this law for a partisan exercise, Republicans are also giving Democrats more ammunition to use in their campaign to overturn the Electoral College in favor of a direct popular vote.

This is the fire Republicans are playing with, no matter their political calculation. Some may figure the vote Wednesday is merely symbolic; they can show solidarity with Mr. Trump’s voters and dodge a primary challenge in 2022. Sens. Josh Hawley and Ted Cruz are making their own presidential calculations for 2024. But the cost of this showboating will be more political cynicism, and a precedent that Democrats are sure to exploit in the aftermath of some future close election.