If I were Trump, I would’ve announced the news conference, but not mention the reason. Why telegraph your punches?
I mentioned this in an earlier post. If he didn't sell it as a big deal, he might not get the audience draw he otherwise would.
If he really has something, he needs millions of eyeballs to see it before the media-liars get a chance to degrade and dismiss it with their lies.
If the fate of the country is hanging on it, he may get an audience big enough to do something about it.
I think he's baiting them to put a gag order on him, which he would probably ignore anyway, and then wait for them to arrest him again. Every time Trump is indicted, an angel gets their wings.