Nevada Gov. Steve Sisolak, a Democrat, vetoed a bill to join a national compact to elect presidents by popular vote, saying that the bill would diminish the state's political power. If Nevada had joined the "National Popular Vote Interstate Compact," which has been adopted by 14 states and D.C., it would mean that the state would award its Electoral College votes to the presidential candidate who won the popular vote nationally.

Sisolak wrote in a letter to the speaker of the Nevada Assembly that the bill would allow the state's electors to "disregard the will of the state's electorate" if a candidate won the national vote but lost in Nevada. He also said that joining the compact "could leave a sparsely populated Western state like Nevada with a greatly diminished voice in the outcome of national electoral contests.

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In a statement, Patrick Rosenstiel, the senior consultant to National Popular Vote, said "we will continue our bipartisan work in every state until the National Popular Vote proposal takes effect and every American voter is politically relevant in every presidential election."

The pact's objective can only be achieved when the states that adopt the legislation collectively have 270 or more electoral votes. So far, California, Colorado, Connecticut, Delaware, Hawaii, Illinois, Maryland, Massachusetts, New Jersey, New Mexico, New York, Rhode Island, Vermont, Washington state and the District of Columbia have signed up for the pact. The number of electoral votes between the group amounts to 189.

Nevada, with its six electoral votes, would have brought the compact up to over 200 electoral votes. Sisolak's objections echo that of many Republicans who support the electoral college because it gives more weight to smaller, more Republican states whose votes would be diminished in a popular-vote system. If elections were decided by the popular vote, then Democrats would have a structural advantage.

The battle over the electoral college in recent years has become increasingly contentious, with some presidential candidates calling for the system to be abolished. Citing the elections of President Trump and George W. Bush, who won the presidency while losing the popular vote in 2016 and 2000, many Democrats have advocated for a change to the way state electoral votes are bestowed.

In 2016, 70,000 votes in three critical states tipped the election to Mr. Trump: Wisconsin, Michigan and Pennsylvania. Since the presidential election is decided by the Electoral College, these votes ended up being more consequential than the 3 million more cast for Clinton, because they gave Mr. Trump the electoral votes he needed to win the election.

Opponents of the Electoral College argue the system concentrates power in smaller states. It also means just a handful of states command the attention of presidential candidates during the campaign. Candidates generally don't campaign in reliably Democratic or or Republican states like New York or Alabama, and instead flock to so-called battleground states like Ohio or Florida, where the race is competitive.