Pennsylvania’s plan would encourage third parties to cherry-pick particular districts, periodically producing “winners” with only national pluralities of electoral votes, leaving the House to pick presidents. The existing system handicaps third parties: In 1992, Ross Perot won 18.9 percent of the popular vote but no electoral votes.

Pennsylvania’s proposal would raise the stakes of gerrymandering. And a swing state such as Colorado would often be neglected: Its nine electoral votes are a pot worth competing for, but under Pennsylvania’s plan, the split might usually be 5-to-4 or 6-to-3.

Winner-take-all allocation of states’ electoral votes enhances presidential legitimacy by magnifying narrow popular vote margins. In 1960, Kennedy won 49.7 percent of the popular vote but 56.4 percent of the electoral vote (303 to 219). In 2008, Obama won just 52.9 percent of the popular vote but 67.8 percent of the electoral vote (365 to 173).