I think there are a few factors at play.

First. I think the ceiling is a hell of a lot lower than it was a few years ago (this goes both ways, would be the same for a MAGA POTUS for sure). Media-fueled polarization (traditional and social), angst about a world that is changing, etc. Demonization is real. Grievance is real. And it is all very ugly, and kinda unAmerican honestly. What is the theoretical max for a Dem POTUS right now? What is it for Donald Trump? Not very high. The historical comparisons aren't terribly meaningful right now unfortunately - where we are (not good).

Second, I think he (and the Dems in general) do an absolute dogshit job communicating with the public. Identifying the things that matter, creating the sound bites, communicating consistently, day in and day out. They have no equivalent of "MAGA" or "sanctuary city", etc. for the topics that matter to voters. It is a problem. He's also pretty low energy, doesn't have very good proxies, doesn't have the propaganda wing (Fox News) that the MAGA GOP does.

A related point. There is absolutely a disconnect between what the (the Dems) think is working and what normal people are feeling. We talk about the stock market a lot. It really is an indicator that has an outsized influence on the narrative given how few people are actually invested... But people care more about what they can afford at the store (on the menu, etc.). Same with interest rates. American people stupidly take out massive loans for cars they can't afford, but more house than they should. There are fewer savers / lenders out there (who benefit from higher rates).

Kitchen table issues matter. A lot. I care about global stability and American influence and prosperity. I care about climate change (it is real people, every private entity in the world has built its impact into their long-range plans). I don't care much about reproductive rights - but what I'm seeing today frightens me. Those are kind of luxury issues to some degree.

I'd say that, in many ways, we're in a much better place than we were a couple of years ago. We don't worry about the pandemic (Sleepy didn't have much to do w it). Inflation seems to be easing (Sleepy didn't have much to do w it). We seem to be managing our economy to a soft landing on the heels of a major period of transition (he should get some credit). We are seeing a renewed focus on international partnership and global stability in the face of a real threat. I give him a ton of credit on that. He botched Afghanistan (he shares blame w his predecessor), we really do have an immigration crisis (he can and should be doing more). I'd grade him out at a B maybe, but even if I move that to a D, there's no way I'd vote for a MAGA candidate to replace him.