Whistleblower filed his complaint in September alleging that Trump made inappropriate requests from the Ukraine president to get assistance in investigating Trumps political opponent (Biden). Also he alleged that the withholding of military aid for Ukraine that was appropriated by Congress was held up by the Trump admin to give them leverage over ukraine so they'd grant this request. He also alleged that people in the White House went to extraordinary lengths to hide the transcripts of these calls because they knew how damaging they'd be.

Last week, the transcript of the call was made public and it corroborated everything in the whistleblower complaint to a tee.

Since then, one of Trump and the GOP main talking points has been that the whistleblower wasn't privy to the call, so his knowledge is 2nd hand and therefore could be false. That argument holds no water though because the transcript and the complaint are both now out for the public to read, and they both say the same thing. So the whistleblower is proven 100% credible, which anyone takes 15 minutes to read the 2 documents can see.

Trump and his allies are banking on people taking their word for it (that the whistleblower is wrong) instead of taking those 15 mins to read the two documents and see for themselves.