I could be way out in left field here, but it could simply be that after so many years with their entire identity wrapped up in that job the prospect of retiring isn’t far off of actual death, psychologically speaking.
Both aren’t necessarily radicalist figures since apparently Biden is considered right wing in Europe and Mitch is apparently a RINO. But most of all, both are senile old men
With Feinstein and Biden likely senile, the US political system at the moment reminds me of the USSR just after Brezhnev except Biden is 1000X fucking less intelligent than Andropov.
Krystal Ball had a good observation on this one: Neither his aides nor his security guy are the slightest surprised or worried by it, suggesting that this happens all the time now.