He's the former Republican governor of California, but Arnold Schwarzenegger isn't ruling out voting for a Democrat in the 2020 election.

During a Monday appearance on SiriusXM’s “Howard Stern Show,” Schwarzenegger was asked if he would be supporting President TrumpDonald TrumpUS, South Korea reach agreement on cost-sharing for troops Graham: Trump can make GOP bigger, stronger, or he 'could destroy it' Biden nominates female generals whose promotions were reportedly delayed under Trump MORE’s reelection next year year.

"I doubt it," he replied with a laugh.

"I could [vote for Elizabeth WarrenElizabeth WarrenSenate rejects Sanders minimum wage hike Philly city council calls on Biden to 'cancel all student loan debt' in first 100 days Hillicon Valley: High alert as new QAnon date approaches Thursday | Biden signals another reversal from Trump with national security guidance | Parler files a new case MORE]," Schwarzenegger said when asked specifically about casting a ballot for the Massachusetts senator if she won the Democratic nomination.

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"I would just have to see what her program is, what her vision is for the future of America, because I think the most important thing is we keep America No. 1,” Schwarzenegger added.

Ahead of 2020, he said, "I will find out what is happening on the Democratic side because I mean there's a lot of weird stuff going on there."

The "Terminator: Dark Fate" star has been vocally critical of Trump, with the two repeatedly sparring on social media. Trump has needled Schwarzenegger for his brief, low-rated period hosting “The Celebrity Apprentice” — which the New York real estate developer used to host — and for his record as California governor.

Schwarzenegger, 72, said in a Men's Health interview last month that the reason Trump had taken shots at him is because "he's in love with" him.

The Austrian-born ex-bodybuilder — who said he voted for then-Ohio Gov. John Kasich (R) in the 2016 White House race — also opened up about his former relationship with Trump.

"He and I used to be friends," Schwarzenegger told Stern, saying the future president was supportive of his 2003 gubernatorial campaign. Schwarzenegger said he declined to accept any campaign donations from Trump because "the money came from gambling" from his casinos.

Ultimately, said Schwarzenegger, a climate activist, "I couldn't really go with him because of his philosophy about the environment and some of the other issues."

"I told [Trump] before the election in 2016, I said, 'Look, I would love to endorse you, but I can't because I worked too hard on environmental issues and you tried to bring coal back. This is like bringing Blockbusters back.'"