Ross Douthat has a good New York Times column on why claims of election fraud have been falling on receptive ears, even among some who are not themselves loyalists of the defeated president. Among points he makes:

• “There is a longstanding pattern in both political parties of gently encouraging conspiracizing. (The Diebold-stole-Ohio theories in 2004 were given oxygen by prominent congressional Democrats; MSNBC’s Russiagate coverage was not exactly cautious in the theories that it entertained.)” Long before 2016, it should be noted, it was Republican oral tradition that big-city Democratic machines would steal votes if given half a chance, a suspicion that has in no way been quelled by dogmatic establishmentarian dismissal of any such concerns as mere “myth.” Trump has voiced these themes in a way that goes beyond any predecessor for vehemence and for divergence from observable truth, but the themes themselves are not new.
• Especially given the resources of the Internet and decline in trust in legacy media outlets, outsider intellectuals today have access to both fame and prestige, as well as inward satisfaction, by trawling through data sets to support provocative contrarian theses tending toward the overall position that Everything They Have Told Us Is Wrong. (See: Covid-19, but many other topics as well.) Election statistics and practices are well suited to data dredging in search of seeming anomalies. Longtime election-watchers will often have a better idea of which anomalies are routine and which might signal actual vote irregularities, but their contributions (say, those of veteran conservative vote-pattern analyst Henry Olsen) tend not to go viral.
• Many people are being radicalized against liberal consensus politics for other reasons. One big factor this year is the onerousness of Covid-19 restrictions, and the perceived hypocrisy of many who support and enforce those restrictions but are willing to set aside the rules when it comes to favored ideological causes or political get-togethers. And once you’re radicalized along one dimension it’s more likely you’ll be radicalized along others — for example, by buying into a hidden-hand, rather than invisible-hand, theory of how the other side manages to stay in power politically despite its flaws.

Recommended, also, is Douthat’s account of how he tries to reason with people in each of the three above groups to find possible grounds of agreement.