Under the Republican plan, if the GOP presidential nominee carries the GOP-leaning districts but Obama carries the state, the GOP nominee would get 12 electoral votes out of Pennsylvania, but Obama would only get eight—six for winning the blue districts, and two (representing the state’s two senators) for carrying the state. This would have an effect equivalent to flipping a small winner-take-all state—say, Nevada, which has six electoral votes—from blue to red. And Republicans wouldn’t even have to do any extra campaigning or spend any extra advertising dollars to do it…

It doesn’t necessarily end there. After their epic sweep of state legislative and gubernatorial races in 2010, Republicans also have total political control of Michigan, Ohio, and Wisconsin, three other big states that traditionally go Democratic and went for Obama in 2012. Implementing a Pennsylvania-style system in those three places—in Ohio, for example, Democrats anticipate controlling just 4 or 5 of the state’s 16 congressional districts—could offset Obama wins in states where he has expanded the electoral map, like Virginia, North Carolina, Colorado, or New Mexico. “If all these rust belt folks get together and make this happen that could be really dramatic,” says Carolyn Fiddler, a spokeswoman for the Democratic Legislative Campaign Committee, which coordinates state political races for the Dems.

Democrats would not be able to retaliate. The only states that John McCain won where Dems control both houses of the state legislature are Arkansas, Mississippi, and West Virginia. West Virginia is too small for splitting the electoral votes to have much effect, and Mississippi has a Republican governor. That leaves Arkansas, another small state—and one where McCain won every district handily in 2008.