(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.

Now imagine what Trump will be without White House advisers surrounding him and at least trying to rein him in. Imagine how he might cast doubt on election results, especially ones that have landed him out of office. Imagine how he might seek to rally support wherever he can find it, even among the most extreme voices in our society. Imagine what he might accuse a successor of doing — especially one who’s just beaten him — given what Trump has said about a predecessor against whom he didn’t even run and who went out of his way to be cordial in the transition between them.
Our nation’s thought leaders need to develop and agree to principles now to mitigate the looming threat posed by ex-President Trump. One might apply to the next president, whether Democratic or Republican: Simply do not engage with ex-President Trump, no matter how vicious his attacks become; isolate him by ignoring him.
Another might govern both sides of the aisle in Congress: Speak up loudly for the norm of ex-presidents treating their successors — and the office itself — with respect, even if they disagree with particular policies. And a third might guide the media: Make a pact (whether or not the likes of Breitbart and Fox News agree to it) not to give ex-President Trump more than perfunctory coverage, whatever invective he hurls and however the public remains fascinated by his norm-shattering behavior.
From the White House to the Capitol to the media, the dangers posed by ex-President Trump put a premium on electing leaders and supporting commentators who can make a compelling — even passionate — case for why fundamental norms of American governance and political dialogue need to be restored and protected.

There will, of course, be more to Trump’s post-presidency than the man himself: He has introduced ideas that will not simply vanish when he leaves the White House. Some of those ideas concern how presidents (and even presidential candidates) communicate, such as by interrupting and talking over debate opponents as well as by using language — like Trump’s reference to “s**thole countries” — previously unacceptable in mainstream politics or even society.
Some of those ideas relate to particular policies, from Trump’s brand of economic nationalism to his insistence that immigration is predominantly a liability for the United States, its security and its identity. No matter how Trump leaves office, those ideas have now been normalized in ways that defy instant reversal. They will need to be addressed by deliberate norm-restoring behavior by future presidents and by the articulation of superior policies by politicians able to make those policies resonate with the public.
Whatever traction Trump’s ideas have, Trump himself will surely cling to the spotlight — if he can. We were, as a nation, largely blindsided by the assault on longstanding norms that Trump has personified. That’s allowed a lot of damage to be done that we’ll spend decades repairing. We can’t afford to be blindsided, yet again, by the potential for ex-President Trump to shatter more norms and continue to shake the foundations of our democracy. That’s what those ousted from power do in banana republics. Let’s get the principles in place to ensure it doesn’t happen here.