Our looming nightmare scenario: What happens if Trump loses in 2020 — but refuses to leave office?

Polls currently show that all the major Democratic presidential candidates are pulling way ahead of Donald Trump, and while Democrats should take nothing for granted — Trump will run a campaign so nasty it will likely put 2016 to shame — there is at least some reason hope that Americans will turn out in large numbers and that Trump will be soundly defeated in 2020. That victory would be both exciting and an enormous relief, a moment when we all collectively begin to believe that the national nightmare is ending.

But as soon as that happens, if it happens, the next nightmare will begin. It may be minutes, hours, days or even weeks, but at some point between Election Day in November 2020 and Inauguration Day in January 2021, odds are strong that Trump will declare that the election was "fake news" and refuse to leave the White House.

This possibility has lingered in the "if" column since he was first elected, largely because Trump is a terminal narcissist whose inability to admit to his own mediocrity caused him to lie his way onto the Forbes 400 list and pretend to be his own publicist in an pathetic effort to generate tabloid coverage of his personal life. Now the prospect that Trump will simply declare the election null and void and refuse to relinquish power to the 2020 victor is better understood to be in the "when" column.

The past weekend was not a good one, in terms of Trump's signaling that he will refuse to accept the results of any election he loses. After internal polls commissioned by the Trump campaign were leaked, showing that the president is trailing badly in several battleground states, Trump angrily called the polls "fake" and fired the pollsters working for him. He also suggested on Twitter that it was possible "the people would demand that I stay longer" than two terms of office, using his joking-not-joking strategy to suggest that he's not hemmed in by laws or the Constitution when it comes to retaining power.

One principal talking point of Democrats who are reluctant to begin an impeachment inquiry is that Trump needs to be removed at the ballot box, not by impeachment. The argument is that Trump can't be removed from office through impeachment since Republicans, who control the Senate, will refuse to convict him no matter how much damning evidence there is. Depressingly, that argument has merit. With vanishingly  rare exceptions like Rep. Justin Amash of Michigan, Republicans have shown that there is no level of criminality Trump could display that they are unwilling to accept, so long as it allows them to retain power.

But that's also why there's a real danger that, if and when Trump refuses to leave office after an electoral defeat, Republicans will go along with it. And why not? They haven't drawn any visible line yet when it comes to Trump cheating or breaking the law. On the contrary, Republicans were already flouting the law in their attempts to retain control over the government even though a majority of Americans have clearly rejected them at the polls. So far, there appears to be no limits to what Republicans will allow, so long as it entrenches their power.

Think about what Republicans were doing even before Trump came along. Gerrymandering and voter suppression efforts predated his candidacy, taking off in earnest after the Republican-controlled Supreme Court gutted the Voting Rights Act. Senate Majority Leader Mitch McConnell also flatly refused to hold a hearing for Barack Obama's Supreme Court nominee, Merrick Garland, violating all norms and traditions to hold the seat open so a possible Republican president could fill it. This trend goes clear back to the 2000 Bush v. Gore decision, in which the Supreme Court's conservative majority handed George W. Bush the presidency rather than allowing a fair and complete vote count in Florida.

Under Trump, Republicans have only become bolder. Robert Mueller's report documented Trump's extensive efforts to collude with a Russian criminal conspiracy to interfere with the 2016 election, as well as Trump's extensive cover-up of that conspiracy. Instead of doing anything about it, Republicans have persistently made excuses for Trump, either lying about what's actually in the Mueller report or drawing false equivalences to legal and transparent choices made by Hillary Clinton's 2016 campaign.

McConnell's response to the Russian criminal conspiracy to undermine the last election, in fact, has been to reject any effort to prevent such conspiracies in the future. Congressional bills have been written to shore up election security and McConnell simply refuses to bring them for a vote. Trump made clear, in his interview last week with George Stephanopoulos of ABC News, that he fully intends to cheat in 2020 the same way he cheated in 2016. McConnell's response has basically been, "Bring it on."

Again, Republicans are so complicit with Trump's criminality that it is simply a statement of fact to note there is no chance that the Senate would vote to convict Trump in an impeachment trial, no matter how serious his crimes are. (A two-thirds majority, or 67 votes, is required, which would require all the Democrats, and aligned independents, plus at least 20 Republicans.) If they refuse to throw him out for being a criminal, why on earth would they throw him out just because he lost an election?

As the saying goes, the best predictor of future behavior is past behavior. Based on that, we must presume that Trump and the Republicans will not be hemmed in by law or custom when it comes to holding onto power they haven't earned. It would be deeply unwise for Democrats to pin their hopes on the possibility that Trump suddenly, after all this time, becomes the kind of man who would admit he lost an election — or that Republicans will finally decide that there's such thing as "going too far" when it comes to taking power in defiance of democratic will.

How do we deal with it when Trump simply declares the election null and void and Republicans back his play? The time to plan for that is right now. Being caught flat-footed and scrambling to catch up will simply make it easier for Trump to entrench the idea that his hold on the White House is immovable, just as he and Republicans have entrenched the idea that it's normal and acceptable for the Senate to refuse to convict him, no matter what.

Unless Democrats move swiftly and forcefully when Trump refuses to leave the White House — and they need to plan for "when," not "if" — Republicans will be able to make forever-Trump feel inevitable and indeed almost normal, as they've done with their other successful efforts at gutting American democracy.