I think he’s the first to do so on the scale of thousands of such statements.

First? No. Most prolific? I think so. He's also one of the first to make heavy use of direct social media, which is different than mass media of old.

Notice also I didn't say Trump, but POTUS in general. What do we want to do here going forward? Should the POTUS be treated differently than a private citizen?

What this current period reminds me of historically is McCarthyism, except we have the POTUS lobbing baseless claims instead of a senator. I don't think McCarthyism impacted the general public as much as claims undermining the election does though.

The problem is not all the claims you might consider baseless actually are and neither you nor I have any way of really knowing.

Which one hasn't, might be a better question.