IIRC, the early consensus wasn't that they were useless, it's that there was no RCT that said they were effective. That's a big difference. Our understanding now is different.

If this was Sen. Paul's only statement--that most masks are ineffective--that would have been a bigger judgement call.

Sen. Paul, however, continued by saying that not only is it a fact they are ineffective, but Dr. Fauci knows this and is thereby lying to the American people.

That's way out of bounds for scientific discourse, and even for differences of opinion in normal discourse.