Donald Trump posed the question to an Iowa audience today of whether he should sue Ted Cruz over his presidential eligibility, "just for fun."

Speaking to a Sioux City crowd, Trump asked, "Should I do it just for fun?"

"It's so nasty though," Trump conceded, before sort of doubling back. "Ugh, I'm so good at this stuff."

Trump and Cruz have sparred intensely over Cruz's eligibility to be president in the closing weeks before the Iowa caucus.

Trump thinks the question of whether Cruz is a "natural-born citizen" is an unresolved question, as Cruz was born in Calgary to an American mother and Cuban father.

Trump has said that it's an open legal question; the Harvard Law grad Cruz says it's an open and shut case. Trump posits that Democrats will sue if Cruz is the nominee.

He appears to not be wrong.

Rep. Alan Grayson, D-Fla., also legally trained at Harvard, has pledged to do just that if the Republicans run Cruz for president.

Trump is currently second in the Washington Examiner's presidential power rankings, with Cruz beating him out for first place.