This is a mistake. I'd agree with McConnell if the President were being impeached on grounds of violation of real laws that have real meaning. But with charges of bribery and extortion dropped in deference to the political ambitions of Joe Biden, the remaining articles are amorphous and partisan. Especially the charge that Trump deserves impeachment because he dares to defend himself and the co-equal powers of the executive branch. Or Nadler's and Pelosi's blather about the need to pre-emptively impeach so he doesn't face the verdict of the deplorable voters.
A motion to dismiss means the charges don't deserve to be taken seriously. A partisan response to a partisan clown show. Good enough for me.