Sen. Elizabeth Warren is warning Democrats to take singer Kid Rock’s potential Senate bid seriously.

The Massachusetts Democrat sent an email blast with the headline “Senator Kid Rock (R-MI)” the Boston Herald reported.

The Michigan rocker, born Robert Ritchie, tweeted on Wednesday that a Kid Rock for Senate website was for real and promised that a big announcement was coming soon. The site, however, is on a Warner Bros. Record URL that sells Kid Rock for Senate merchandise. Doubters speculated that Ritchie was drumming up publicity for a tour or a restaurant he’s opening in Michigan.

Still, Warren, a favorite among the liberal wing of Democrats, said the party should worry about Ritchie, comparing his potential run to that of President Donald Trump.

“I know a lot of people are thinking: this is some sort of joke, right?” she wrote in her email. “But we all thought Donald Trump was joking when he rode down the escalator at Trump Tower and announced his campaign, too.” 

Warren reminded supporters that just as Ritchie might be pulling a stunt to sell more albums, everyone thought Trump was just trying to promote his television show “The Apprentice.”

Ritchie is considering challenging Michigan Democratic Sen. Debbie Stabenow next year. A native of the state, his name has been teased by some in the state’s party as a potential candidate in the past.

The fundraising page Warren linked to in her email split donations between Stabenow and Warren, who is also up for re-election next year.

Warren has also faced the specter of a outspoken Republican celebrity as former Boston Red Sox pitcher Curt Schilling weighed a challenge to her. But Schilling looks likely to pass as he has endorsed Senate candidate Shiva Ayyadurai.