Conservative commentator Ann Coulter, who has been supporting Donald TrumpDonald John TrumpRed states find there’s no free pass on Medicaid changes from Trump Trump meets with Moon in crucial moment for Korea summit The Memo: Trump flirts with constitutional crisis MORE for president, took to Twitter on Wednesday to declare that Sen. Ted CruzRafael (Ted) Edward CruzSenators near deal on sexual harassment policy change Senate GOP urges Trump administration to work closely with Congress on NAFTA Five Republican run-offs to watch in Texas MORE (R-Texas) is not a natural born U.S. citizen.

Coulter joins Trump in questioning whether Cruz can legally be president.

“Republicans are going to have to ask themselves the question: ‘Do we want a candidate who could be tied up in court for two years?’ That’d be a big problem,” Trump told The Washington Post on Tuesday.

The U.S. Constitution states that to be eligible for the White House, one must be a “natural born citizen.” That’s long been interpreted to include anyone born to a U.S. citizen, even outside the country.

Cruz was born in Canada to an American mother and Cuban father. For years he held dual U.S.-Canada citizenship. The Texas Republican renounced his Canadian citizenship after he became a U.S. senator.

Cruz has laughed off the suggestion he’s not eligible for the White House, taking to Twitter on Tuesday to post a link from the television show “Happy Days” that shows the character Fonzie on water skis jumping over a shark.

Cruz and Trump are battling atop the polls in Iowa with less than a month to go before the caucuses there.