Why would Trump announce it? Everybody knows it already.
The guy was a Republican until 2015. He switched to a Dem to run for office.
Maybe Trump is announcing that he is a Democrat!!!!
Seriously though, this should be illegal. The guy ran on as a Democrat and should have to remain a Democrat until he finishes his term.
Being forced to be a democrat is a very severe punishment.
What difference does it make whether he is affiliated with democrats or republicans? There might be something, but I'm not aware of any differences. During the Reagan years, a LOT of democratic congressmen changed to the republican party so that they could be re-elected.