There are two books that literally have dropped in the last 2 weeks and the authors have been doing a lot of media about them. One is called “Fight: Inside the Wildest Battle for the White House” another is called “Uncharted: How Trump beat Biden, Harris, and the Odds in the Wildest Campaign in History”. Both of these books quote anecdotes from Biden admin insiders and dem politicians about the challenges they saw and experienced.

DNC fundraiser Lindi Li has been all over the podcasts and news (back in November a lot) talking about the challenges she saw.

I’m not sure what you consider “reliable news sources” but I have seen this topic and these authors, and Lindi Li on network, cable, and new media news sources across the spectrum.