Trump didn’t file the lawsuits. And there is no indication the suits are being filed on behalf of Trump in any way.
Trump tried to get Cruz to head this off. But Cruz either refused or dallied.
The entire thing is a "when did you quit beating your wife scenario?"
Actually, Trump urged Cruz to obtain a declaratory judgment in federal court. Federal courts will not issue a declaratory judgment unless there is an actual case or controversy involving the requesting party, as opposed to a theoretical controversy.
So until there is an actual case or controversy involving Cruz in the federal judicial system, Cruz can’t obtain such a declartion.