Conservative commentator Ann Coulter, who has been supporting Donald TrumpDonald John TrumpJustice Department preparing for Mueller report as soon as next week: reports Smollett lawyers declare 'Empire' star innocent Pelosi asks members to support resolution against emergency declaration MORE for president, took to Twitter on Wednesday to declare that Sen. Ted CruzRafael (Ted) Edward CruzO’Rourke not ruling out being vice presidential candidate CNN ripped for hiring former Republican operative as political editor: 'WTF?!?!' The Hill's Morning Report - Can Bernie recapture 2016 magic? 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.