Wikipedia on Declaratory Judgement
"A declaratory judgment is typically requested when a party is threatened with a lawsuit but the lawsuit has not yet been filed;"
Too late for Cruz now. The lawsuit has been filed.
I once told a few here what it is about ‘declaratory judgements’ you posted, but they predictably pooh poo’ed it.
He was born a citizen. There's some parsing about smoke stirrers and armchair attorneys who think that a treatise is the same as law and that there's a difference between someone born a citizen and someone who is a "natural born" citizen.
Courts are not going to get in the middle of that if the issue isn't 99% correct (non citizen, residency, etc). "Don't like him beat him in an election" is their view.