In fairness to Sen Klobuchar (whom I happen to support, but I agree hasn't much of a chance), her seat's not up for reelection next year so she's not risking it by running for Prez. And honestly, the Democrats in the Senate pretty much have nothing to do these days. McConnell railroads through what he wants to pass without their help, and bottlenecks everything else. The minority party is little more than a placeholder under current Senate rules, with the small exception of the very few times a supermajority is required.
Those are a different stripe. Bullock is term limited out of running again as governor, and Hickenlooper is already out of office, each in a state with a chance to unseat a Republican Senate incumbent.
Joe S. needs to get his ego in check. He may be a lapsed Republican, but he isn't a Democrat. He and all the never-Trumpers are really quick to tell the Democrats what to do, but haven't a clue how to repair the party they've fled.