Washington (CNN) Nevada Democratic Gov. Steve Sisolak on Thursday vetoed a bill that would have seen his state join a growing movement to effectively convert presidential elections to a popular vote system.

The state's Senate voted last week to approve a bill passed earlier in the State Assembly that would add Nevada to the National Popular Vote Interstate Compact, an agreement among states to allocate their electors to the winner of the popular vote once a controlling number of states have joined together. On Thursday, Sisolak issued a letter to the State Assembly offering his formal veto message rejecting the bill.

Sisolak's opposition is a blow to the movement that has picked up steam in the wake of President Donald Trump's win in the Electoral College over Democratic nominee Hillary Clinton, who defeated him in the popular vote. The compact, if successful, would make the winner of the national popular vote the winner of the Electoral College and therefore the winner of the presidential election, rather than the current system, where most states award all of their electors to the winner in each given state.

In a Twitter thread explaining his decision, Sisolak said the compact "could diminish the role of smaller states like Nevada in national electoral contests and force Nevada's electors to side with whoever wins the nationwide popular vote, rather than the candidate Nevadans choose."

"In cases like this, where Nevada's interests could diverge from the interests of large states, I will always stand up for Nevada," Sisolak said.

In cases like this, where Nevada's interests could diverge from the interests of large states, I will always stand up for Nevada. (4/4) — Governor Sisolak (@GovSisolak) May 30, 2019

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