A third-party account on the contents of a partially overheard phone call, or one they were told about second-hand, is hearsay. There is a specific legal standard here.
Only the two parties involved on the phone call and knowing the entirety of its contents can testify to what was said. In order to verify the statement they would have to cross-examine McCarthy, Trump or both. They did not, therefore the contents of the call would be inadmissible in a *real* court proceeding and summarily tossed in the trash.
In a real court proceeding, neither side would be allowed to
meet with the jury in private and Trump's lawyer for today would probably be chucked into another court on around five to ten different perjury charges for all the blatant lies he spewed.
And even if that one bit is hearsay... what about the rest? There's mountains of evidence proving that the Capitol riot was a direct result of Trump having spewed years of inflammatory rhetoric, months of lies about the election results and a solid month or two of encouraging his supporters to "stop the steal" and "fight like hell [to change the election results]".
By the time Trump himself refuses to testify or comment or just provide information on a single shred of this, it should be pretty obvious that the reason thereof is because if he did testify, he'd either be lying under oath (more perjury) or incriminating himself.
The only reason Trump, who loves talking about himself to no end oh so much, would have to decline to testify or comment... would be that he did what they're accusing him of. Otherwise, why wouldn't he testify? A guy practically obsessed with himself would surely LOVE to show his side of the story in order to 'own the libs', right?
All the Republican Senators that voted to acquit... are basically victims of an abusive relationship.
They don't want to call him out or help to make him get what he deserves, because if they do that then he'll lash out at them and make things worse for them with the help of his fanatic base of madmen. (That last bit is rather special and basically exclusive to this case, as most other abusers aren't
the fucking President abusing his own Congress while wielding a follower base that checks every single box on the definition of a cult of personality.)
So they deny everything, inadvertently helping fool decent chunks of the masses into doing the mental gymnastics necessary to earnestly believe he's innocent and could do no wrong.
They deny everything, and the result is that everyone in the situation suffers except the abuser.
They acquit, and the result is that everyone in the nation suffers except Trump.