|Data from major polls taken since November 21, 2019
If you combine Biden and Buttigieg's numbers and Sanders and Warren's numbers the Centrists and the Communists are in a virtual dead-heat: 34.7% vs. 33.8%
Biden's polling shows the most bounciness with a standard-deviaiton of 7.0%. Standard deviation is a common way to characterize variation. Warren's polling has the least variation with a standard deviation of 3.1%
The correlation matrix also tells us that Sanders and Warren's polling numbers have a correlation of +0.43. A positive correlation suggests that their numbers move in tandem like the tide raising and lowering all boats. Clearly, certain states and pollsters love their (nearly) identical message and other states/pollsters are less enamored.
To date, there has been little to put Sanders/Warren into a zero-sum-game like Biden-Buttigieg. That is likely to change after the first primary and it becomes a cage-fight to collect delegates. At that point, if I were Sanders, I would not drink from the teacup Warren handed me.
Strategically, the Democratic kingmakers have to be thinking of a ticket that is Biden + Sanders OR Warren or Warren + Buttigieg. In the first scenario, I think Warren will get the nod because of age and stability in polling.