And one thing we can be sure of as the election approaches: Donald Trump is not going to change.

Given that Mr. Trump’s approval rating has been hovering around 40 percent throughout his presidency, his obvious and only strategy is to turn his dial further into the red. He will try to raise the stakes by painting the election as a choice between himself and a radical, left-wing apocalypse. He will bay about socialism, open borders and “deep state” corruption and relentlessly work to inflame and exploit racial and cultural divides.

But as Mr. Trump seeks to rev up his base, he also runs a significant risk of driving away a small but decisive cohort of voters he needs. His frenetic efforts to create a panic over the immigrant caravan in the days leading up to the 2018 midterms may have stoked his base, but it also generated a backlash that contributed to major losses for his party.

With everything on the line and nothing, to his mind, out of bounds, the same dynamic will be in play in 2020, and this creates an opportunity for Democrats — if their party’s message allows Trump defectors to comfortably cross that bridge.

There is a legion of arguments on moral, ethical and policy grounds for Mr. Trump’s defeat, and that’s leaving out the sheer incompetence. But the most effective question for Democrats to get voters to ask is simply whether the country can survive another four years like this.

Can we continue to wake each day to the tweets and tantrums, the nasty, often gratuitous fights and the ensuing turmoil that surrounds this president? Can we make progress on issues of concern to the way millions of people live their lives with a leader who looks for every opportunity to divide us for his own political purposes? And is a Trump freed of the burden of re-election really going to be less combative and more constructive in a second term? Um, no.

Each time Mr. Trump lashes out, as he will with increasing ferocity and frequency as the election approaches, these questions will gain more resonance. Every erratic escalation — every needless quarrel, firing or convulsive policy lurch — will provide additional evidence in the case for change.

Mr. Trump’s impulse is always to create a binary choice, forcing Americans to retreat to tribe. He wants to define the battle around divisive cultural issues that will hem in his supporters, and it would be seductive for Democrats to chase every tweeted rabbit down the hole. The president would welcome a pitched battle over lines of race, ideology and culture.