Regional politics. Right now, the Electoral College pushes campaigns to expand the “map,” reaching out to build a geographically broad coalition.This is why the Trump campaign strategy of outreach defeated the Clinton campaign strategy of sitting on its presumed lead. Clinton received more popular votes, but Trump built a broader national coalition—which the Electoral College rewards. Without this incentive, NPV would set the United States drifting toward more regional politics and would exacerbate existing divides.
Plurality winners. The Electoral College requires a majority, not just a plurality, of electoral votes in order to win. This has the effect of driving people to build massive, nationwide coalitions (the two major political parties). Under NPV, any popular vote plurality—no matter how regional or how small—would be good enough. This would make it easier to run “spoiler” candidates, increasing the risk of campaigns gaming the system and of small plurality winners (for example, with five candidates, the winner might have less than 30% support).
Recounts? NPV is incompatible with existing state recount laws, but includes no provision for recounts. In a close national election with concerns about mistakes or fraud, NPV provides no legal framework for a recount. The margin could be razor-thin nationwide, but not close enough in any state to trigger a recount.
Election insecurity. NPV gives more power to states with lax election laws. Vermont allows felons to vote from prison and cities in California and Maryland have begun to allow non-citizens and even illegal aliens to vote in some elections. With NPV, every ballot that can find its way into the ballot box means more power for that state. Voters would be forced to trust—without any power to verify—the honesty of other states’ elections.
State upsets. Under NPV, a candidate could “win” a state’s electoral votes without even being on the ballot in that state. The NPV compact requires a state to appoint Electors for a candidate who received a tiny percentage of support in that state, or even to a candidate not on that state’s ballot, if the candidate won the most votes nationwide.
State dropouts. NPV claims states cannot drop out of the compact close to an election, which would upend the campaigns and could manipulate the outcome. But whether this clause is enforceable, and who would enforce it, is uncertain.
Reapportionment. Every ten years, the census results in some states gaining, and other states losing, congressional seats and presidential electoral votes. For example, current NPV states have slow population growth and are thus set to lose a few electoral votes. Because of these changes, the NPV compact could either take effect or be deactivated without state legislative action, but simply because of reapportionment.