Yeah, Klobuchar will be the "most radical socialist Democrat candidate ever" if she runs. So would Bloomberg. Just like Biden would have been or Buttigieg or maybe even Sanders. The right-wing will attack them all as being radicals. Selling it will be easier with Sanders, but the difficulty wouldn't stop the GOP from doing their best.
I don't know why anyone still believes the 90s line about reaching across the aisle to appeal to the middle. The Republicans haven't accepted a meaningful olive branch from the Democrats in more than a decade, and not for lack of
endless offers during the Obama years. Any attempt to look more Republican-friendly will just hit a solid wall of propaganda.
Especially if it is interpreted as an attempt undermine Trump. He's purging his own party of the disloyal right now, you think he's not going to send his attack dogs after whoever takes the Dem nomination? Republican legislators get chastised in the rightwing media if the are so much as spotted having a friendly conversation with a anti-Trump politician, let alone working with them on something. There isn't enough folksy charm in the world to absorb the firepower, both literal and metaphorical, that is about to be unleashed on the liberal candidate. No quarter, no compromise. There are only two kinds of people in Trump's world: Americans and never-Trumpers.
You want to win over the middle, offer them something that is in
their natural self-interest, not something that the Republican Party wants. That's why Yang and Bernie get along with right-wing libertarian types better than middle-of-the-road wishy-washy types do. They talk to people, not parties. It's part of why Trump himself was popular in the electoral college game. Say what you will about the man, but he's no partisan puppet.