If were a total fabrication, don't you think Mr. Big Lawyer Cruz would be launching a lawsuit for libel for millions of dollars? If Cruz says nothing about a lawsuit (and he hasn't so far), then we can be sure the story is true.
My understanding is that politicians have little recourse to libel laws. Something would have to be particularly egregious before they could achieve any sort of success in court. Private individuals have far more ability to sue than do public personalities.