He's been a complete failure of a President; the US is in terrible shape. I could go over a hundred reasons how he failed but his supporters are enamored by him he can do no wrong. So why bother. 186,000 Americans died due to Covid and he's presenting it as an excellent result. It's absurd but hell if Americans bought the whole WMD thing why not try ?
That being said, he's going to lose the election. Not enough Americans drank the kool aid the deplorables that live off his every word don't get to vote 3 times. There are massive groups of people that lost any confidence in him ages ago. Many women, minorities, farmers, people with dying relatives, people who lost their jobs because of needless tariffs and/or Covid for example. Maybe he can avoid the embarrassment of a landslide loss.
Please keep in mind that my comments are narrowly focused on Trumps' convention speech. As I noted before conventions are basically "preaching to the choir"; they are usually only watched by those who strongly support the candidate and only sway unaffiliated voters when something drastically goes wrong.
The post convention polling "bounces" are short term and nearly meaningless. More of America (including unaffiliated voters in swing states) tune into the debates. The polling after the debates is much more meaningful in regards to how the general election will go.
I will note that the polls are narrowing as we get closer to the election. As noted by 538 and other professional poll watchers -- it would be foolish to count Trump out despite his rather poor record over the recent four years.