If a former president, now out of office (RIIIIGHT, DEEP STATE?), now a private citizen, can be put through an impeachment trial..... then why did Richard Nixon resign?!

After all, he did so in order to avoid certain impeachment in the House and all-but-certain removal by the Senate. Leaving office voluntarily while he could. You can't fire me, I quit! The moment he announced his resignation everyone knew that it was OVER, at least as far as that particular prospect went.

Nixon, like Trump, was a proud man and a fighter. A very different style of fighter, but he still HATED to lose. And just as they do Trump, the Democrats hated Nixon with a venom that was personal. They were out to humiliate and personally destroy him.

If the Democrats of 1974 (who at the time held much bigger majorities in both houses than they do now) had thought that they could still put him through the entire impeachment circus AFTER he'd quit, they'd damned well have done it. And if Nixon had thought they'd do THAT to him he'd never have bothered resigning, because he'd have had nothing to lose by staying and fighting.

But instead Nixon stood down, and Congress stood down, because the idea of a post-presidency impeachment never occurred to either party. Because that idea is complete and utter un-American banana-republic bullshit.