Countries in Trump’s crosshairs have found few ways to fight back against a president who appears dug in on owning Greenland, patrolling the Western Hemisphere, and bullying Europe. One thing they do have, Bridgewater’s Ray Dalio told Semafor’s Liz Hoffman: A lot of America’s bonds.

The $9 trillion of US debt owned by foreign countries is an “enormous vulnerability,” Dalio said at Semafor Haus in Davos. His warning came as global investors finally appeared spooked by Trump’s actions, and stocks and bonds tumbled. An executive at Denmark’s largest pension plan said it was selling off its $100 million in US Treasury bonds — a move he insisted wasn’t political — after Trump doubled down on his Greenland demands.

“You could easily imagine it could simply become unpopular to buy or hold US debt,” Dalio said. (The hedge-fund founder promptly urged the audience to buy gold.)

This isn’t the first time the US’ reliance on global bondholders has become a weakness: In 2007, Russia suggested to Chinese officials that they simultaneously dump their holdings of Fannie Mae bonds, then-Treasury Secretary Hank Paulson wrote in his memoir.

A PIMCO executive told the Financial Times that the bond giant was pivoting away from US assets because of Trump’s “unpredictable” policies, and General Atlantic’s co-president told Bloomberg TV that “for the first time in our 45-year history, we have more assets outside the US than inside.”