She underperformed Clinton last year, I mean she was the only incumbent democratic senator to do so (with Menendez). She is toxic with white non college voters, and would underperform in wealthy suburbs, nominating her would be a gift to Trump.
And Republicans nominating extremist Ronald Reagan was a gift to Jimmy Carter.
And Democrats nominating draft-dodging philanderer Bill Clinton was a gift to Bush sr.
Nominating a wing candidate is MUCH more dangerous for democrats than for republicans for at least three reasons:
1) Conservatives are inherently more tribal than liberals and WILL gather around their leader almost no matter what, as seen in 2016 where Trumps favourables were in the dumpster even amongst republicans before he became the nominee and they basically all turned out for him.
2) Democrats have much more of a turnout problem due to having a larger share of low-propensity voters. These people are much more likely to sit it out if the nominee isn't exactly thei cup of tea than republicans.
3) It is much easier to fearmonger against a left-winger in america than against a right-winger which has been seen time and time again. The "socialist" label is toxic overall, even if it isn't amongst those under 35. Hell, even the "liberal" label isn't all that sellable. Democrats almost always have to run on being some sort of "moderate" who isn't going to take all of your money, whereas republicans can freely run on being "conservative".
This is why I am a left-winger who always support moderate democrats.