WASHINGTON • United States presidential hopeful Donald Trump returned to his political roots this week by questioning whether one of his rivals is even eligible to become president.

This time, his target is Senator Ted Cruz, the Republican national polls runner-up who may pose the greatest threat to his nomination.

Mr Trump is taking a different approach: Rather than flat-out insisting that Mr Cruz is disqualified from the presidency, as he did in 2011 with the Hawaii-born President Barack Obama, the real estate developer is claiming to be concerned that Mr Cruz's Canadian birthplace could get his candidacy tied up in the courts.

"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," Mr Trump told the Washington Post in an interview published on Tuesday.

He continued: "I'd hate to see something like that get in his way. But a lot of people are talking about it and I know that even some states are looking at it very strongly."

While the courts have not ruled on the issue, legal scholars agree the qualification for the presidency under the United States Constitution that the candidate be a "natural-born citizen" applies to a person born to a US citizen parent regardless of where the birth took place. Mr Cruz was born in Canada to an American mother and Cuban father.

The salvos underscore the shifting relationship between the New York tycoon and the Texan senator as they find themselves vying for the lead in the Republican presidential race. Initially, they avoided criticising each other.

But things have changed.

Mr Trump dominated the Republican pack in a recent Reuters/Ipsos national poll, but Mr Cruz leads the field in Iowa, the first state to hold its presidential nominating contest next month.

BLOOMBERG, REUTERS