By Jon Keller

BOSTON (CBS) – Tonight’s the night for the first presidential debate, and especially if you’re not at home to watch it, please, go easy on the drinking games. I shudder to think of the public safety hazard afterwards if folks have chosen “radical” or “lie” as their prompt.

There will be two more of these after Tuesday night (plus a vice-presidential debate), but this is the big one. Voting is already underway, and there are very few undecideds available to be won over. Unlike 2012, when incumbent President Barack Obama sleepwalked through his first debate with Mitt Romney, there is no reservoir of personal esteem that Donald Trump can draw on to coax a second or third chance from voters.

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Any election involving an incumbent is always in large part a referendum on that incumbent. And Trump comes into tonight with unprecedented political baggage, from the dishonest, botched pandemic response to the news that he pays far less income tax than you do for no good reason.

The president’s sycophants and the candidate himself have been backing away from their summer-long spin that feeble old Joe Biden will melt into his Depends on the debate stage. And while it’s unclear if this has penetrated the self-delusional fog surrounding the S.S. Trump, he can’t just stand there and belittle Biden the way he did Hillary Clinton.

So what can Trump do to extract positive energy from tonight?

• Run like a challenger. Swing voters are more likely to enjoy a revival of 2016 Trump, the feisty outsider looking to challenge a moribund establishment, than they are to respond to 90-minutes of whining about the media, name-checking Hunter Biden and Tara Reade, and pretending our national problems don’t exist.

• Steal attack lines from Biden’s fellow Democrats. Quote Kamala Harris on Biden’s anti-busing past, Julian Castro on the Obama/Biden immigration record, Eric Swalwell (remember him?) on generational obsolescence. The point is not that Trump holds superior positions on any of this, but to remind low-information voters that even members of Biden’s own party found him severely wanting, until they didn’t.

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• Give the folks at home a fresh plot twist. This will never happen given the aforementioned fog, but what a shock it would be to conventional wisdom if Trump were to show some humility, however feigned?

Have we made some mistakes handling this crisis? Yes, it’s unprecedented. But we’re on track now with testing, supplies and treatments, and a change of administrations won’t help the process.

OK, maybe that’s bogus. But it might have more of a prayer of success than the usual barrage of bluster.

And as for Biden? He has a much simpler task. All he has to do it make it about Trump, his serial falsehoods, his invisible ethics, the administration’s rank incompetence. Take a cue from Sen. Elizabeth Warren’s campaign and answer any question about what Biden will do with go to my website where there’s a detailed plan – but I can tell you what I won’t do [fill in reference to whatever Trump did here].

And when Trump goes on the attack, Biden should be ready with at least ten different versions of the same response: for God’s sake, stop it, don’t you realize how sick to death the American people are of your dishonesty and vulgarity?

It may turn out that tonight’s debate and those to come are relatively meaningless, that the cake is baked and its just a matter of counting the votes (gulp). But that doesn’t mean it’s not must-see TV.

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Watch it on WBZ-TV and CBSN Boston starting at 9 p.m., then catch my instant analysis on the WBZ News at 11.

Jon Keller