As others have noted, Democrats have more appeal when people are struggling to make ends meet, while Republicans do better when other things like immigration and foreign policy are on the forefront. There are exceptions like Reagan 1980, but it's an exception. But economies have a way of rebounding when they're down, so Democrats on balance leave the economy better than they found it -- in part because of chance, but in part because Democrats are more likely to supercharge growth through Kenyesian stimulus policies. So Democratic presidents deserve some credit, but it's also in part because of how the political cycle tends to swing.
But now I'll be mean to the Republicans. In recent years they've abandoned even the semblance of sensible economics in favour of this absolutely neolithic "guverment bad, spending bad, smol goverment make big economy ooga booga" nonsense. It stems from Reagan's economic policies, which might have made sense given the unique economic struggles of the time, but it's gone off the rails since. HW saw that contractionary policies were needed, raised taxes, and was punished for it. Since then, it's always been tax cuts with the Republicans including when it made absolutely no sense, like the Trump tax cuts. These aren't sensible conservatives like Dewey and Rockefeller, they've just accepted this economic fundamentalism that leaves the country worse off when crises hit. When governments are unable to respond to economic crises, the crises get worse. If the GOP actually had the balls to go to a completely laissez-faire approach, then fine, just leave government intervention out of it. But they've adopted a mantra of endless spending and lower taxes which clearly is a bad combination.
There's also the fact that a lot of cuts under Republicans have been to the internal operations of government and not necessarily to program spending.
Fareed Zakaria has a good take on this. More sensible conservative governments like Merkel's CDU, which did pursue quite sweeping austerity during the start of their term - although in the last decade or so, in part because of their coalition with the social democrats, they've moved to the left. However, one thing they kept strong was the German Public Service. So when a crisis like COVID strikes, they have the tools in place to mount a swift and effective response.
But American agencies are horribly underfunded and completely unsuited to respond to crises. Democrats are pretty good when it comes to keeping these things intact, but Republicans gut government left and right. So when a crisis like COVID, or the 2008 recession, or Katrina struck, Republican administrations were awful at mounting an effective response because of their own disbelief in government. Ironically, this means the per-dollar effectiveness of Republican spending is much lower, and economies suffer.
