REPUBLICANS AREN’T alone in manipulating election rules or drawing districts to favor their candidates, but lately they’ve been in the vanguard. Their latest proposals, to fiddle with presidential vote-tallying, are particularly egregious. Following through on them not only would damage the GOP’s reputation but also could drain all legitimacy from the electoral college system. Virginia Republicans, thankfully, killed such a reform plan Tuesday. Republicans elsewhere should stay away, too.

State-level GOP leaders around the country have been considering ways to split up their states’ electoral college votes, and one idea is to do it according to congressional district maps. A presidential candidate who wins a congressional district, say, would win one electoral college vote.

Advocates claim their proposals would make the process more democratic. The electoral college results from a 51-to-49 state would reflect in some way the preference of the 49 percent, instead of awarding all the state’s electoral college votes to the candidate who squeaked out a narrow statewide victory.

In reality, though, these proposals would replace fixed electoral boundaries based on history — state borders — with constantly shifting ones based on different geographical factors and partisan calculation — gerrymandered congressional district lines. If applied to the last election, President Obama would have taken only four of Virginia’s 13 electoral votes, instead of all of them. True, the candidates would have campaigned differently, too. But this system applied nationally would give Republicans a built-in advantage because it would dilute the influence of highly concentrated urban voters, who tend to vote Democratic in large numbers. These effects are uncertain, though, because partisan redistricting in the future would certainly change the electoral map.

What’s more alarming is the unequal effect of only some states moving to a district-based or similar system. Republicans might switch the system in Democratic-leaning swing states but keep the winner-take-all standard in reliably red states — a result conceivable because of widespread GOP control of state legislatures and governorships. It is not accidental that these proposals have traction among Republican politicians in states Mr. Obama won in the last two elections.

At the least, an already complex electoral system would get more so. Election results would probably become less reflective of national sentiment. And, as RealClearPolitics’s Sean Trende points out, the country would be in store for recount after recount, since victory margins in close congressional districts would hinge on even fewer votes because of the smaller vote totals.

All of that would destabilize the already imperfect electoral college.