To his rally-goers, Donald Trump openly craves a 2020 showdown with Sen. Bernie Sanders (I-VT), salivating at the prospect of getting to run against an elderly, self-declared democratic socialist.

But in private, his view of a potential run against the senator is a lot more complex and less swaggeringly self-assured.

Those around the president say he’s been of two minds when the topic of facing Sanders in 2020 comes up. While he sees the senator as a vulnerable opponent, he also has offered begrudging respect for his political acumen. Trump will—sometimes unprompted—bring up Sanders’ own working-class support, and acknowledge that there is, in fact, potential for the senator to win over Trump voters with his populist appeal, three sources who’ve discussed this with the president tell The Daily Beast. The president has been impressed with Sanders’ ability to ignite his base and draw a large crowd, though not, in his words, as “good as Trump.” The president has also privately discussed the fundraising hauls that Sanders and his campaign have pulled off, noting Sanders’ impressive track record with small-dollar donors.

“In my conversations with the president, both in interviews and privately, I get the sense the president has clearly taken notice of the amount of money that Sanders is raising, the amount of small donors, and the passion of his followers,” said Eric Bolling, a BlazeTV host and friend of Trump and his family.

The respect the president has shown for Sanders is, in a way, a reflection of Trump’s own belief that the key ingredients for success in American politics are unconventionality and populism. Sanders, like the president, has cast himself as a politician who operates outside the traditional governing structures and whose north star is helping the American working class.

But while Trump has been quietly impressed by Sanders, aides and confidants say he doesn’t view him as an electoral threat, at least not yet. Bolling, for one, said Trump views a Sanders nomination as “a gift to his re-election campaign because he believes America is not ready for a socialist president of any kind.” And others who’ve spoken to Trump in recent months say that the president still expresses a desire to run against the senator, or someone of his ideological stripe, in part because it would easily afford him numerous lines of attack: from tying Sanders’ left-wing rhetoric to the economic crisis in Venezuela, to pushing caricatures of the Green New Deal, to warning of far-left government takeovers of major U.S. industries.

“President Trump would love to run against Bernie Sanders because President Trump believes he would crush Bernie at the ballot box and be able to hit him over the head with his socialist rhetoric from now until the election,” said Jason Miller, Trump’s former comms director for the presidential transition.

In public, Team Trump has adopted this bring-it-on posture. The president has gone after Sanders several times this month on his preferred social-media site, dubbing the senator “Crazy” while predicting that he, along with former Vice President Joe Biden, would be the likely Democratic nominees.

But the calculation is a bit more nuanced behind closed doors. When Trump talks to friends and advisers about Sanders, he often will note that Sanders drew far bigger (and more uproarious) crowds than Hillary Clinton did in 2016. Miller even recalled that candidate Trump, during the 2016 race, would convey a “respect” for Sanders that was rooted in their mutual “distrust of the establishment.” Miller also recounted how candidate Trump talked about how “he never heard anyone clap for Hillary Clinton the way they clapped for Bernie.”

Sanders, for his part, has made no secret of his desire to draw voters from Trump’s coalition with an ideologically different flavor of anti-establishment messaging. Last week, the senator went on Fox News, the president’s favorite cable news network, to conduct a town hall meeting that was a thinly veiled attempt at reaching and converting Trump supporters.

The town hall was, from both a ratings and messaging perspective, a success. It also appears to have irked Trump, who lashed out publicly at Fox News.

For Sanders’ campaign, Trump’s social-media flailing was vindication of their strategy. It was also taken as evidence that the president would find it difficult to run against the senator should the two end up in the general election.

“We got in his head,” campaign manager Faiz Shakir told The Daily Beast on Friday. “It did seem like a bit of a panic and a bit of fear that came through his tweets and rightly so. Because I do think what you saw in the Fox News appearance was what will end up being a very intentional and successful outreach by Sen. Sanders to voters who may have either voted for Donald Trump, may have had some sympathy or empathy towards him, and have since soured on him.”

“Donald Trump, for as wild as his Twitter account is, I do think that what you get out of it is a sense that he understands that Bernie Sanders is a bit of a wild card,” Shakir added. “[He] doesn’t know how to deal with him.”

Sanders’ aides had anticipated that the town hall would be a mixed affair, with some supportive audience members but others who would jeer and boo, too. Instead, the crowd mostly applauded as the senator touted policies like Medicare for All, and didn’t register much dissatisfaction when he criticized Trump as a “pathological liar.” It’s a term Sanders uses in private about the president as well. On the car ride over to the town hall, Shakir recalled Sanders saying that Trump was such a liar that he can’t “even tell a straight story about where his dad was born”—a reference to the president erroneously stating that his father migrated from Germany.

The independent from Vermont wouldn’t say that he respects Trump’s political abilities, but acknowledges that “it will not be a cakewalk to defeat him,” Shakir said.

Sanders is clearly approaching this run for office differently than the campaign he ran four years ago. There is much more focus on presenting himself as a formidable general-election candidate. And there’s a greater sense of responsibility placed on defeating both Trumpism and Trump. At a recent event, Shakir recalled a woman who spoke with Sanders and had broken down as she recounted how difficult things had been for her during this administration. Shortly after that exchange, Sanders turned to his campaign manager and stressed just how important it was that they unseat Trump.

“There’s people out there whose hopes and fears are resting on us doing this right,” Shakir recalled Sanders saying to him. “We have to make sure we are doing everything right on this campaign.”