The quote:
“Given Joe Biden’s incredible record, given Donald Trump’s terrible record: he should be mopping the floor with Donald Trump. Joe Biden is running against a criminal. It should not be even close. And there is only one reason it is close. And that is the president’s age.”
The problem is that Republicans don’t vote for a candidate they vote for a party. The Republicans could run Hitler’s reanimated corpse as their candidate and as long as it had that R next to its name it would get their vote. Democrats on the other hand are much more likely to not vote for or not even show up to vote at all for a candidate they don’t particularly like. It’s why good Democrat candidates always beat Republican candidates of any kind, but bad candidates usually lose. Democrats massively outnumber Republicans, but the Democrat party nearly always runs the worst possible candidate. If Republicans win any election it’s not because they had a good candidate, it’s always because Democrats ran a bad one.
My pet theory is that the establishment wing of the party (that largely controls the DNC) wants to have a specific coalition that keeps them in power within the party. Like, if Democrats wanted to be the party of the working class or appeal to rural voters, they could but would require leadership that isn’t from New York, San Francisco, or other similarly rich places.
So, under the leadership of Clinton, Pelosi, and Schumer, they chose to make the swing voters the ones they appeal to most. Maybe Bernie’s positive populism would have matched up better against Trump’s negative populism than Clinton’s outdated neoliberalism. But leadership and the DNC would rather lose an election and keep control than win but lose their place atop the party hierarchy.
I think it’s simultaneously less conspiratorial and more nefarious than that: the establishment wing of the party likes power and power means control over campaign funding, so they pander to large corporate donors by suppressing anti-corporate populists.