Republican presidential contender Donald Trump on Sunday said he’d consider filing a lawsuit challenging GOP rival Ted Cruz’ constitutional eligibility to be president, based on his birth in Canada.

“That’s an interesting case, wow. That sounds like a very good case. I’d do the public a big favor,” Trump said on ABC’s “This Week” when host George Stephanopoulos asked if he’d consider filing a lawsuit.

Pressed by the host about whether he’d file a lawsuit, because he’d have standing an opposing candidate, Trump said, “I’d like to talk to Ted about that, let’s see how he’d feel about that.”

Cruz has said questions over whether he meets the constitutional test of being a “natural born citizen” are without merit. The Texas senator was born in Calgary, Alberta, where his father, originally from Cuba, worked in the oil industry at the time. His mother was a U.S. citizen. He moved to the United States at age 4.

Cruz, meanwhile, did not back away for attacking Trump for “New York values,” citing an interview Trump gave in 1999 citing he was open to abortion and other socially liberal positions because he was raised in New York.

“It is amusing seeing the media elite in New York and D.C. run around with their hair on fire wondering what on Earth are New York values? I’ll tell you and the rest of the country, people understand exactly what that is,” he said on “Fox News Sunday.”

Trump, on “This Week” called Cruz a “hypocrite” for raising money in New York and taking personal loans from banks for his 2012 Senate campaign that he didn’t disclose on Federal Election Commission forms, including a loan from Goldman Sachs.

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“You know why? He wants to look like Robin Hood that he’s the one protecting the people from the banks while he’s actually borrowing money and personally guaranteeing it and not disclosing it, which is illegal,” Trump said.