( CNN) Someday, Donald Trump will become ex-President Trump. After a guilty plea from his longtime “fixer, ” Michael Cohen, alleging that Trump directed the commission of federal crimes, perhaps that day will arrive sooner rather than later. But whether it's a week, 18 months or more than six years away, we need to start preparing now. That's because, for all of the threat to our democracy Trump poses as president, he may pose an even bigger one as an ex-president.

No one knows how Trump will leave the Oval Office. Maybe he'll resign. Maybe he'll be impeached. Maybe he'll be voted out in November 2020 — or maybe he'll leave at the end of two terms in January 2025.

But, however he becomes an ex-president, it's impossible to imagine Trump following in Richard Nixon's post-presidency footsteps — ones that literally traversed empty beaches in a solitary existence.Whether Trump leaves of his own accord after eight years or is abruptly cast out by a vote of the Senate or Electoral College, he is not one to go quietly into the night.