Historically he outperformed all the polls. We will see this time.
Nevertheless, Joe Biden beat him by a comfortable margin in 2020, and Democrats outperformed their polling in 2022, where the president's party traditionally has done more poorly than the opposition. This has been an extremely unusual election season, and Kamala Harris's emergence as the Democratic nominee was a gamechanger. She quickly caught up with and passed Trump's polling numbers. Now there appears to have been some leveling, as the initial wave of enthusiasm for her inevitably waned. She did not get the traditional bump in polling from the Democratic convention, but her numbers have been holding fairly steady.
Bear in mind that almost all of the pollsters use models that do not report raw numbers, but numbers weighted according to the demographic of the individual answering the poll. What we do not know is what voter turnout will be like and whether there will be a surge in, say, the number of young voters, which would favor Harris. We also know that a small percentage of Republicans will vote for Harris, and some ticket-splitting will take place. Will people continue to feel that inflation or the border situation are strong issues for Trump, or will the super hurricanes make people more concerned about climate change than they have been in the past?
There are an awful lot of variables that can affect results, including the weather conditions on November 5. And early voting appears to be really strong this year, which should be a modest advantage for Harris. I dropped my own ballot off yesterday, just a couple of days after I received it in the mail. There was no doubt in my mind about who I would vote for, so there was no point in delaying. OTOH, my state was always going to prefer Harris, so I could have sat it out, if I were more apathetic about elections.