“Definition of affidavit - a written statement confirmed by oath or affirmation, for use as evidence in court.”
In court, the affidavit and person making such is open to cross examination.
A sworn affidavit, in of itself, is not proof. At least until it stands up to cross examination.
but it is still better than the crap that the media said was credible when they were attacking Trump. That’s the point.