Republican strategist Karl Rove, the man behind both of George W. Bush’s successful presidential campaigns, thinks Democratic contender Bernie Sanders could beat Donald Trump in 2020 to become the next president.

After watching the Vermont senator’s Monday Fox News town hall, Rove complimented Sanders on Fox and Friends Friday, saying participating in the event was a “smart move on his part.” He was also impressed with the response Sanders got, saying, “Bernie comes on to Fox, and gets the largest viewership of any campaign event thus far.”

Karl Rove breaks down why Bernie Sanders could win the 2020 nomination https://t.co/fAA1JlM52F @FoxNews #AAG — All American Girl (@AIIAmericanGirI) April 19, 2019

Rove’s appearance on Fox News followed an editorial he wrote for the Wall Street Journal, in which the former White House deputy chief of staff argued Sanders proved himself a “serious contender” during the town hall because of how he directly answered questions — from both the moderators and the audience — about his tax returns, health care, and his electability in the large field of Democratic candidates vying for their party’s nomination.

When it came to answering questions about his taxes, Rove said Sanders was succinct and on-message, showing he learned valuable lessons about parrying tough questions and connecting with audiences during the 2016 Democratic primary.

Just before taking the stage at the town hall, Sanders released the last 10 years of his tax returns, and urged the president to do the same. When asked about these returns during the town hall, Sanders said, “I pay the taxes I owe.” He then used a question about his status as a millionaire to attack Trump’s tax plan, arguing “83 percent of the benefits went to the top 1 percent — I think that’s a bad idea,” before advocating for higher taxes for the wealthy.

Rove also complimented the 77-year-old senator’s answers when confronted with the argument that he may too old for the office, with moderators asking whether the party might be ready for a “new generation of leadership.”

“He makes a joke, he says it’s a fair question,” Rove said, “He says, ‘It’s not whether you’re young, it’s not whether you’re old. It is what you believe.’”

Sanders self-identifies as a democratic socialist, and Rove, who told the Fox and Friends audience “socialism ain’t pretty,” even found something good to say about the parts of the senator’s appearance that addressed democratic socialism.

“He did a good job of softening the edges of socialism,” Rove said. “He made it feel warm and fuzzy, kumbaya, let’s shake hands around the campfire.”

However, the Republican strategist wasn’t completely glowing in his analysis of the Democrat, arguing in his Wall Street Journal piece, “Such platitudes go only so far in masking what drives Mr. Sanders’ philosophy: resentment, grievance, and a desire to take from those who have and redistribute the wealth, all to expand government. He may describe socialism in benign terms, but he regularly drops his guard, opening himself up to devastating counterpunches.”

What happened during the Fox News town hall?

Sanders took questions from the network’s anchors Bret Baier and Martha MacCallum and from the audience. As Vox’s Dara Lind pointed out, the senator turned both sets of questions to his advantage:

When speaking directly to audience members or to the TV audience watching at home, Sanders was sincere and open. When asked about President Donald Trump, he spoke with emotion about how he hoped everyone could agree a “pathological liar” should not be president; in his closing statement, he practically begged for more comity in the country, without backing off his insistence that the rich need to do more to provide for working families. When speaking to Baier and MacCallum, however — or, in a couple of moments, directly to the Fox News-watcher-in-chief — Sanders was as prickly as you’d expect. “The president watches your network a bit, right?” he needled. He hectored the hosts for making more money than he did. He huffed that he’d give fair answers only if asked fair questions.

Sanders also won over his audience. When the moderators asked the town hall’s participants to raise their hands if they were in favor of Medicare-for-all, something Trump has criticized, and a fair number of audience members raised their hands, cheering loudly. This visibly surprised the Fox News anchors.

Raise your hand if you're sick and tired of your private health insurance company. We need Medicare for All. #BernieTownHall pic.twitter.com/3euHRCjqn9 — Bernie Sanders (@BernieSanders) April 15, 2019

This reaction, and Sanders’s performance overall, has Rove thinking Trump needs to keep an eye on Sanders.

After seeing his performance Monday, Rove doesn’t believe the Democratic primary will work in the same way it did in the last election. In his Wall Street Journal piece, Rove said beating Sanders by attacking his democratic socialist views “won’t be as easy as Republicans may think.”

And according to the strategist, Sanders is increasingly on the minds of Trump campaign officials. “Some of the Trump campaign people said ‘You know what? We’re paying attention to this guy,” Rove said. “We’ve got to take him seriously.’”