Arnold Schwarzenegger endorsed Vice President Kamala Harris on Wednesday, saying that Donald J. Trump’s efforts to overturn the 2020 election were disqualifying and that electing Ms. Harris was the only way to reduce division and anger among Americans.

Mr. Schwarzenegger, the actor and bodybuilder who served as governor of California as a Republican from 2003 to 2011, said in a lengthy statement on social media that he hated what United States politics had become and was tempted to “tune out,” and echoed the sentiments of many voters in writing that he didn’t like either party at the moment. He criticized Republicans’ economic policies as opposed to free markets, and said he believed Democratic policies would increase crime.

But in his statement, he wrote in reference to Mr. Trump’s words and actions: “Rejecting the results of an election is as un-American as it gets. To someone like me who talks to people all over the world and still knows America is the shining city on a hill, calling America is a trash can for the world is so unpatriotic, it makes me furious. And I will always be an American before I am a Republican.”

So, Mr. Schwarzenegger said, he would vote for Ms. Harris and her running mate, Gov. Tim Walz of Minnesota, as a repudiation of Mr. Trump. Mr. Schwarzenegger then detailed a string of criticisms of the former president.

He said Mr. Trump wouldn’t respect votes if they weren’t for him and showed no ability to work to pass any policy besides a tax cut for wealthy people. He also noted that Mr. Trump has described Americans who disagreed with him as bigger enemies than China, Russia or North Korea.

Mr. Schwarzenegger added that he disagreed with many of Ms. Harris’s and Mr. Walz’s proposed policies, but that he was convinced that electing them was the only way “to move forward as a country.”

Ms. Harris has been courting endorsements from well-known Republicans like Mr. Schwarzenegger who are willing to argue publicly that this year’s election is about principles that are more fundamental than policies. She has campaigned in several battleground states this month alongside former Representative Liz Cheney of Wyoming, an anti-Trump Republican who has made a similar argument.