This Is Water
That 25% number is an absolute minimum. But more importantly that 25% would elect the people in power.
No, it won't. There's another 30% of hardcore Trump supporters you're ignoring.
I didn't make that claim. I pointed out the obvious: It's a reason to doubt any single poll.
It's a reason to doubt polling in general, yes. Specifics need to be demonstrated.
My position is that it isn't logical that Biden would benefit as much from Sanders or Warren dropping out as the Sanders or Warren survivor.
No one has said Biden would benefit as much from Warren/Sanders dropping out as either of the other two. Morning Consult didn't say that either. A plurality of Warren/Sanders voters would likely switch to the other. But Biden will receive a sizeable minority of either cohort.
It didn't take me long to find a poll to support my position:
The YouGov polling 11/2/19 conflicts with the poll you offered.
That Biden's strength as the second choice is the lowest of the three leading candidates makes perfect sense.
Biden 1st choice 25.6 + 2nd choice 8.5 = 34.1
Warren 1st choice 25.1 + 2nd choice 13.6 = 38.7
Sanders 1st choice 14.3 + 2nd choice 10.3 = 24.6
The Impact of Voter Second Choices as 2020 Dems Drop Out | RealClearPolitics
You didn't read carefully. The math you copied and pasted is aggregating all Dem voters' first and second choices, not just the first and second choices of Biden/Sanders/Warren voters. Second, this poll was taken when Warren was surging, so it puts her essentially tied with Biden for first choice. That is not the case anymore, not even close.
When you drill down to second choices for specifically Warren/Sanders voters, these results are very much in alignment with the Morning Consult polling:
The second choice for supporters of the two most liberal candidates is typically (and unsurprisingly) the other liberal. Pluralities of Warren and Sanders supporters list the other as their second choices, with 24% of Warren supporters choosing Sanders and 36% of Sanders supporters choosing Warren (nearly 35% of each candidate’s voters indicated they had no second choice).
So as I said, a plurality of around 30% of the Warren/Sanders folks say they'd opt for the other as a second choice.
Here's another recent Quinnipiac poll finding much the same thing:
The only way these numbers pan out to a lead over Biden for either Warren or Bernie is if several other candidates drop out and the majority of those cohorts pick them over Biden.