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Democrat Joe Biden takes the stage at the first presidential debate of 2020 on Tuesday staring at an opponent, President Donald Trump, who has unwittingly done him a big favor — lowered expectations for Biden's performance.

The president has spent months painting Biden as sleepy, doddering and senile, a move that may have lowered the bar for Biden's performance in the eyes of many voters who will be seeing him on stage in Cleveland for the first time since the Democratic convention.

An even passable performance by the former vice president might come off looking like a win in a debate that has taken on outsize importance after COVID-19 limited the candidates' in-person campaigning.

"President Trump will definitely try to throw the vice president a bunch of curveballs that are designed to get him off his game," said Jay Carney, who was Biden's communications director before becoming White House press secretary under President Barack Obama. "The vice president fully expects and is preparing for that and knows that taking that bait is not what he wants to do."

But if the gaffe-prone Biden stumbles, or looks even a little like the caricature Trump has painted of him, his campaign may be damaged. There are two more presidential debates to go, but first debates — like first impressions — have a way of sticking to candidates.

A good debate performance by Trump at Case Western Reserve University in Cleveland could help revive his faltering campaign. He's trailing Biden by about 7 points nationally, according to an average of polls by RealClearPolitics. Trump, bolstered by his unwavering confidence in his ability to sell himself, has said he's done little of the traditional preparation for a high-stakes debate. He says his daily back-and-forth with reporters, sometimes two or three times a day, is practice enough.

"I think I prepare every day. I think, you know, when you're president, you sort of see everything that they're going to be asking," Trump said in a Sunday interview with Fox News.

Trump muddied the waters a little more on Sunday, tweeting a "demand" that Biden take a drug test before or after the debate — the latest in a series of baseless suggestions that the former vice president's public appearances have been affected by drug use.

But first debates are often a trap for incumbent presidents, who have less time for practice than their rivals.

Ronald Reagan devastated President Jimmy Carter in 1980 by asking voters if they were better off than they were four years ago. President George W. Bush was criticized for complaining about how hard his job was while debating John Kerry in 2004. Bush's father, President George H.W. Bush, faced double-barreled attacks from Bill Clinton and independent Ross Perot in his first re-election debate in 1992 — and famously looked at his watch mid-debate. President Barack Obama, one of the Democratic Party's most gifted orators, was clearly bested in his first debate with Mitt Romney in 2012.