How large are the various groups of potential voters? [View all]
Specifically, of those who will or may vote Dem, how would you rank each group in terms of its size/likely impact?
1) First off, you've got the mass of Vote Blue No Matter Who/party faithful.
2) There's a lot of talk about "independents," but we know from multiple studies that the vast majority of them consistently vote a straight-party ticket (Dem-leaning indies vote Dem and Rep-leaning indies vote Rep). They're partisan but hate partisanship, as one article on the subject stated. They're also not as reliable voters (and quite possibly not as informed) as the party-affiliated.
3) Next, there's, I think, a pretty substantial number of folks who will either not vote or will vote 3rd party unless we nominate Sanders (or possibly Warren). They feel that the US is in desperate need of large-scale fundamental change. They, many of them young, feel disenchanted or downright pissed off. Like it or not, that's pretty evident.
4) As for "independents" who might be classified as true swing voters, I think they're definitely the smallest lot of the bunch that I've mentioned so far. It's also hard to say exactly why they might vote a certain way. Some claim that they'll support the most moderate option, but that's disputed by the following article, which suggests that "confused" would be a more apt description: https://fivethirtyeight.com/features/the-moderate-middle-is-a-myth/.
5) Lastly, there are Republicans who could potentially vote Dem. Personally, I think that's a tiny and inconsequential fraction of the electorate.
We probably take a hit with one group by going after another. It's doubtful that we can get great turnout from each and every group. Sacrifices will be made, and one's perception of how large each group is would seem to dictate where one thinks sacrifices should be made.