Billionaire Jeff Gundlach told fellow wealthy investors late Tuesday that Sen. Bernie Sanders is the “odds-on favorite” to win the 2020 Democratic presidential nomination—and warned the senator’s potential general election victory could pose a serious threat to Wall Street profits.

“Bernie is stronger than people think,” Gundlach, who correctly predicted Donald Trump’s defeat of Hillary Clinton in the 2016 presidential election, said during his annual “Just Markets” webcast.

Gundlach, CEO of investment firm DoubleLine Capital, said Sanders’ possible win over Trump in November represents the “biggest risk” to financial markets.

“I think it’s Bernie Sanders becoming more believed in as a real force, and we have to start taking him more seriously,” Gundlach said. “If people get more worried about Bernie Sanders and they start to price in his spending programs, then you could really start to see trouble in both [long-term Treasury] bonds and stocks, which could really be on a rough ride.”

Asked by CNN reporter Ryan Nobles about Gundlach’s assessment of the 2020 race, Sanders’ communications director Mike Casca offered a snappy response: “A stopped Rolex is right twice a day.”

Gundlach’s remarks came as the Democratic establishment is reportedly growing increasingly concerned about the prospect of a Sanders nomination as the Vermont senator outraises his primary opponents and gains ground in early-state polls.

“Bernie Sanders has just pulled even with Joe Biden in Iowa and is beating him in New Hampshire, giving Sanders a reasonable claim to being either the frontrunner or the co-frontrunner for the 2020 Democratic nomination,” Current Affairs editor Nathan Robinson, a vocal supporter of the Vermont senator, wrote Wednesday.

“Bernie has struck fear into the heart of the establishment, and even more moderate commentators like Chris Cillizza have noticed that Sanders is in a very good position now,” Robinson added. “Bernie Sanders also has a strong case to make that he is the most ‘electable’ candidate in a race against Donald Trump.”

Sanders attempted to make that case in an op-ed Wednesday in the Des Moines Register with less than a month to go before the Feb. 3 Iowa caucus.

“Iowans face a choice: Are we going to settle for a status quo that is leaving so many behind? Or are we going to come together to finally transform our country so that our government works for all of us?” Sanders wrote. “Our grassroots campaign clearly represents the latter—which is why polls consistently show us defeating Donald Trump, who is the most dangerous and corrupt president in modern history.”

Invoking his campaign’s “Not Me, Us” motto, Sanders said “to transform America, we cannot simply rely on a president alone—we must build a mass movement that fights for justice not just during an election, but once we are in office.”

“We are building that movement,” the senator wrote, “and with Iowans’ help on Feb. 3, we can start making this working-class agenda a reality.”