Not impeachable.
And running for office should not ever protect someone for selling their government office in the past.
There were many losers cut from the first Dem debate pools and others whose names are dimly recalled if at all. Biden waited to enter the race for a few months and sent out his sappy video to declare.
Thus, all the Dems now can claim immunity from any criminal investigations? Biden isn't any more the final actual winning nominee at the 2020 convention balloting than Mayor Pete and Warren are. All hopefuls. So no one can now charge any of them with a crime as it will look like trying to cut down a political rival?
All these cannot have their dealings if any with Ukraine or China looked into :John Hickenlooper, Jay Inslee, John Delaney , Seth Moulton, Howard Schwartz and Tom Steyer. Political rivals all.