She is acceptable to the widest range of primary voters
The Democratic primary is coming down to a 3-way contest between Biden, Sanders and Warren.
Biden is on the moderate left, he is unacceptable to progressive left voters. Sanders is on the progressive left, he is unacceptable to moderate left voters.
Warren sits perfectly between them and is acceptable to everyone. She is the first-choice candidate for centre-left voters and the compromise second-choice candidate for voters at either end. If Sanders’ support drops it will move to Warren. Likewise, if Biden’s support drops it will also move to Warren.
Creepy Uncle Joe will lose
It will be difficult for Biden to recover after an opponent makes negative adds of him being handsy and inappropriate with little girls.
Joe Biden is a moderate old straight white male, exactly what the progressive left of the Democratic party wants to get away from. At the most recent (4th) debate there were times when he could hardly string a sentence together. With the constant attention of a long campaign, it’s inevitable that the 76-year-old with have some bad senior moments.
The early front-runner based on name recognition rarely wins. Over the long campaign, other candidates’ name recognition will increase while Biden’s is already at its maximum.
Comrade Sanders will lose
Bernie Sanders reached his peak popularity last time around and it was not enough. Everyone who is going to be a Sanders supporter is already a Sanders supporter, he is a known quantity.
Sanders is also an old straight white man. At 78 years old he recently had a heart attack.
Sanders is too progressive for the moderate wing of the Democratic party and he loses a lot of the progressive vote to Warren.