Do boring, sensible, centre right politicians not exist any more?
Dead as the dodo, at the national level. John Kasich was the last of the breed, and it wasn't working for any of them. Romney lost, McCain lost, Bush 43 was well right, Dole lost, Bush 41 lost once he was off coattails, Reagan was well right, Ford lost.
The last center-right nominee elected purely in his own right was Nixon, and he lost in '60. Democrats win by running to the center, but Republicans win by turning out their lunatic fringe. The stock answer as to why is racism, but the explanation takes some untangling.
If the Green Party and Cornel West go forward as candidates that has to be bad news for Biden, surely?
Green always pulls from the Democrats, the way Libertarian mostly pulls otherwise Republican voters. West isn't good for Biden, and never was. The question is how many votes either will get in the states that matter when push comes to shove. This early, third party polling is best conceived of as 'interest' rather than a firm vote.