I suspect we'll see it played out in court. To your point, Cal, one could argue that since he was Impeached as President, he must be tried as President. And to your point, Rummy, yes, once the Impeachment fuse was lit, the trial becomes a must. In fact, if the Senate tries to dodge, xPDJT would be within his rights to demand it!
In the final analysis, SanFranNan et al failed to heed Yamamoto's admonition and the Giant is awakened.