Why are Democrats having such a "hard time beating Trump"?

That's the question posed by the official publication of the prudent wing of the ruling class, i.e., The New York Times.  I'll return to the NYT article in a moment, but a rather different answer is found in this paper that philosopher Gordon Barnes called to my attention:  globalization has been good for both the prudent and imprudent wings of the ruling class; it has not been so good for millions of working class people in the U.S.

But back to the NYT:

The Democrats’ challenge appears to be part of a broader trend of political struggles for ruling parties across the developed world. Voters appear eager for change when they get the chance. The ruling parties in Britain, Germany, Italy, Australia and most recently Japan all faced electoral setbacks or lost power. Mr. Trump himself lost four years ago. France and Canada might well join the list.

Trump lost because the pandemic and resulting job losses put the electorate in a foul mood.  Some of the other countries involved triumphs by the (modestly) "left" party, not a party of the reactionary right, like Trump's Republicans (Italy comes closest, and Germany may yet join that club).  According to the NYT, while 

The specifics vary from country to country and party to party, but much of the story is the same: the pandemic and upheaval that followed. Nearly everywhere, high prices and the fallout from the pandemic left voters angry and resentful. It discredited ruling parties — and many of them weren’t especially popular at the outset.

This gradually eroded and sometimes shattered trust in government officials, liberal elites and the media. When prices rose, it frustrated millions of younger and low-income voters who saw their savings, purchasing power, housing opportunities and hopes dwindle.

These are causal claims, for which no evidence is adduced, although the inflation effect does seem like a real one based on prior work.   One suspects, however, that much of this is a "how things look to the prudent wing of the ruling class" analysis, rather than a serious, systemic one--again, the contrast with the paper on the domestic vicitms of globalization and Trump support makes for an instructive contrast.  (Voters who had genuine economic grievances and voted for Trump were making a serious mistake, of course:  but desperate people do desperate things.)