Bernie Sanders warned that the same wave of populism that gave rise to the Brexit movement could shape the outcome of the 2016 election, unless Democrats “wake up” and try to do something about it.

“The notion that Donald Trump could benefit from the same forces that gave the Leave proponents a majority in Britain should sound an alarm for the Democratic Party in the United States,” Sanders wrote in a New York Times op-ed on Wednesday. “Millions of American voters, like the Leave supporters, are understandably angry and frustrated by the economic forces that are destroying the middle class.”