Biden fielded the first question from moderator Jake Tapper, who asked him what his message was to Americans who feel worse off financially under his administration than they did under Trump.

Biden claimed he was handed an economy in "free fall." He touted his record on job creation and lowering prescription drug prices and other household costs.

Trump, in turn, claimed he he had "the greatest economy in the history of our country" and that inflation is "absolutely killing us."

Biden and Trump are now at the lecterns. The two entered from different sides of the stage and did not shake hands.

ABC News Senior Congressional Correspondent Rachel Scott reported that Melania Trump will not be at the debate.

The former first lady has made few appearances on the campaign trail as her husband seeks another term.

Biden posted a photo on x taking a shot at Trump's allegations that he's taking performance-enhancing substances for the debate.

The president is seen holding a can of water with the "Dark Brandon" meme image claiming to be "Dark Brandon's secret sauce." The can, which will go on sale on the Biden campaign's site next month, has a statement in bold letters "Get real, Jack. It's just water."

"I don't know what they've got in these performance enhancers, but I'm feeling pretty jacked up. Try it yourselves, folks. See you in a bit," the X post said.

After tonight's debate, there will be a rush to anoint a "winner" and a "loser," but the only way we can really do that is once we have data on how the debate will actually affect people’s votes. To that end, 538 partnered with Ipsos to poll the same group of likely voters both before and after the debate to see how their attitudes change. Here are some of the key findings from our pre-debate poll, which was conducted using Ipsos' KnowledgePanel.

First, we asked respondents to rate how well they thought each candidate would perform in the debate tonight on a five-point scale. On average, Trump got a score of 2.96 out of 5, and Biden got a score of 2.58 out of 5. In other words, expectations are significantly lower for Biden tonight, which could end up helping him -- even a so-so performance from Biden would exceed most people's expectations.

It looks like the reason people have such low expectations for Biden is his advanced age. We also asked respondents to grade each candidate's physical, mental and emotional fitness on a five-point scale. On average, Biden got just a 2.3 out of 5 on physical fitness and a 2.4 out of 5 on mental fitness. Trump bested him on both of those measures, but Trump got only a 2.6 out of 5 on emotional fitness, which was lower than Biden's score.

We also asked voters what issues would have the most impact on their vote. Fifty percent ranked inflation or increasing costs as one of their top three issues, while 37% included immigration. Voters also said Trump would do a better job handling those issues than Biden, so it will be especially important for the president to show strength on these issues tonight.

Finally, we asked voters which candidates they were considering supporting. Heading into the debate, 44.8% of voters are at least considering voting for Trump, 44.5% are at least considering voting for Biden and 18.5% are at least considering voting for independent candidate Robert F. Kennedy Jr., who failed to qualify for the debate. (Respondents could say they were considering multiple candidates, which is why these numbers add up to more than 100%.) We'll ask voters the same question after the debate to see whether these numbers shift.

-538's Nathaniel Rakich