Senior Republicans say they will try to leverage their party’s majorities in Democratic-leaning states in an effort to end the winner-take-all system of awarding electoral votes. Instead, bills that will be introduced in several Democratic states would award electoral votes on a proportional basis.

Already, two states — Maine and Nebraska — award an electoral vote to the winner of each congressional district. The candidate who wins the most votes statewide takes the final two at-large electoral votes. Only once, when President Obama won a congressional district based in Omaha in 2008, has either of those states actually split their vote.

But if more reliably blue states like Michigan, Pennsylvania, and Wisconsin were to award their electoral votes proportionally, Republicans would be able to eat into what has become a deep Democratic advantage.

All three states have given the Democratic nominee their electoral votes in each of the last six presidential elections. Now, senior Republicans in Washington are overseeing legislation in all three states to end the winner-take-all system.