If Democrats want to beat Donald Trump in the general election, they must think pragmatically, not ideologically. This election will be determined by Independents and Moderates, both Republican and Democrat.
The progressive/socialist wing led by Warren and Sanders cannot garner these voters. Bernie has baggage that Trump will expose. His history includes supporting Ortega, Castro, Socialist Workers Party and the Soviet system.
This will turn swing voters off. Warren waves her hand and says she can fix anything. While Bloomberg wants to buy the election with his billions, Warren & Sanders want to buy the election with taxpayer trillions.
Mayor Pete, while his military service is admirable, has never accomplished anything on the national stage -- zilch, nada. Small town mayor to the leader of the free world is a big stretch.
Biden already has two failed presidential runs. The only other candidate to distinguish herself is Amy Klobuchar. She has, from the beginning, advocated for a bigger tent for the Democratic Party. She's considered a moderate, giving her access to the voters needed to win.
She can shut Trump out except for those in his base. Klobuchar is a grass-roots candidate who has earned her place with hard work. Plus, there's an attractive sound to the first woman POTUS.