Conservative commentator Ann Coulter, who has been supporting Donald TrumpDonald John TrumpTillerson: Russia already looking to interfere in 2018 midterms Dems pick up deep-red legislative seat in Missouri Speier on Trump's desire for military parade: 'We have a Napoleon in the making' MORE for president, took to Twitter on Wednesday to declare that Sen. Ted CruzRafael (Ted) Edward CruzSasse statement: Trump nominee who spread conspiracy theories has a ‘tinfoil hat’ Coalition of 44 groups calls for passage of drug pricing bill For the sake of our democracy, politicians must stop bickering 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.