The challenge to debate by Cruz was a childish move. Cruz knows full well that the RNC would not approve a debate outside the agreed upon rules. As far as the eligibility issue is concerned, it is as serious as a heart attack. There are substantive issues surrounding the definition of natural born citizen as it applies to eligibility for the Presidency. It has never been litigated with Constitutional scholars coming down on different sides re Cruz.
Is Ted Cruz a 'natural born Citizen'? Not if you're a constitutional originalist