This week’s debate between President Biden and Donald Trump won’t produce much in the way of civil dialogue over the nation’s future. It’s more likely to resemble a demolition derby, with each contestant trying to knock the other off course.

And, let’s face it, many viewers will tune in mainly for the crashes.

The question isn’t who will win that series of collisions — it’s who will lose.

Presidential debates rarely transform an election. But Thursday’s showdown could change the momentum in this year’s contest — mostly because the stakes for Biden are so high.

The president is running about even with Trump in national polls, but he’s behind in the battleground states that will determine the outcome. He’s also battling the view among many voters in both parties that he’s too old to serve effectively for another four years.

Republicans have waged a relentless campaign to stoke those doubts. Biden “can’t put two sentences together,” the former president told supporters last month. “He can’t find the stairs off the stage.”

That’s a pretty low bar for Biden to clear. Last week, Trump belatedly realized his mistake and tried to reverse course, calling the president “a worthy debater.”

“I don’t want to underestimate him,” he explained.

Either way, the 90-minute debate will give the 81-year-old president an opportunity to show that he can not only find the stairs but think on his feet as well. If Biden doesn’t visibly pass that test, his campaign will have a hard time recovering.

Trump, who is 78, faces challenges too.

In his first debate against Biden in 2020, the then-president behaved like a disruptive bully and promptly dropped four points in the polls.

A similarly chaotic performance this week in Atlanta would help revive the anti-Trump coalition of voters that fired him last time.

If Trump blunders badly — he has been known to lapse into incoherence and confuse Biden with former President Obama — he too would face renewed questions about his mental fitness.

Again, the question isn’t so much who will win but who will lose. Candidates fail in debates by stumbling more often than they triumph through brilliant wordplay.

So the stakes are high for both candidates. The incentive will be to go on the attack, to try to push the other guy toward disaster.

The debate, hosted by CNN with correspondents Jake Tapper and Dana Bash as moderators, will spare viewers the tedium of opening statements. There will be no live audience, a demand Biden’s side made after witnessing the noisy enthusiasm of Trump supporters at earlier events. Each candidate’s microphone will be silenced while the other is speaking, in an attempt to avoid a repeat of the 2020 debate, when Trump constantly interrupted Biden and the moderators.

I asked strategists from both parties what advice they would give each candidate.

Biden’s first task is to “demonstrate that he’s not too old to serve another term,” said Doug Sosnik, who advised President Clinton during his 1996 reelection campaign.

After that, Sosnik said, Biden “needs to have a clear narrative about his presidency, what his goals would be for a second term. And then he can go after Trump.”

Republican strategist Alex Conant agreed that Biden should try to steer the debate toward the future and away from a referendum on his stewardship of the economy, which has left most voters dissatisfied.

“He needs to make the debate about abortion and everything else Trump doesn’t want to talk about,” Conant said. “He should try to provoke Trump into overreacting … then get out of the way and let Trump destroy himself.”

One pitfall Biden needs to avoid: boasting about legislation he has passed or trying to convince voters that the economy is better than they think.

“He has to prosecute his political case against Donald Trump and not get bogged down, as incumbents often do … in defending his record,” said David Axelrod, who advised Obama during his 2012 reelection campaign.

Trump’s goals, no surprise, are pretty much the reverse of Biden’s. He wants to make the election a referendum on Biden’s first three years.

“My advice to Trump would be: ‘You are going to win this race on two issues: inflation and immigration. Those are the only two things you should be talking about,’” Conant said.

If the moderators or Biden ask Trump about his conviction on 34 felony charges in New York state, “he doesn’t need to engage in it,” Conant said.

Sosnik agreed. “Stick to a referendum,” he said. “Were you better off during [Trump’s] presidency or Biden’s?”

The hazard Trump needs to avoid: lapsing into complaints about the 2020 election, his conviction or his three pending criminal cases. That would reinforce the appearance “that he is only out for himself and settling old personal scores … [and] reminding people how chaotic and exhausting his presidency was,” Sosnik said.

So will Thursday’s debate change the direction of the race? Conant, the Republican, thinks it could.

“This is the most consequential debate we’ve had in recent memory,” he said. “Voters have major questions about each candidate. There’s an unusual number of undecided or third-party voters who might still be movable. If one of the candidates has a really bad night, that could be decisive.”

But Sosnik is skeptical that many undecided voters will bother watching “a debate between two candidates they dislike.”

“It will take a big moment where one of the candidates falls on his face to make it a game changer,” he said.

With four months remaining before election day, one evening in June won’t determine the winner. But Thursday could provide a pivotal moment — depending not on which candidate performs better but which performs worse.

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