Seems fairly plausible, but why put this specifically in terms of the Democrats? The same will apply to the Republicans, or any other party anywhere whose support comes from anything other than a perfectly homogeneous group.
The Republicans are less of a coalition than the Democrats, and more an alliance of two groups; social conservatives, and economic liberals.
On the face of it, that should make her more likely to get nominated. Are you suggesting that the Democratic Party's electorate is sufficiently calculating to reason: "She's doing these things to get nominated, they seem likely to piss off Sanders supporters, that will hurt us in the general election, so I won't vote for her in the primary"? Colour me unconvinced.
This isn't why Sanders will win, this is why he's still behind. It's a short-term strategy, however, which she started too soon; the primary voters aren't going to vote against Hillary because they don't think they'll win in the general election, they're going to vote against Hillary because she's alienated them to pander to her base.
The Republicans are less of a coalition than the Democrats
So what? If your argument is "if they achieve group G's goals, group G will be unmotivated because they've already got what they need; if they don't, group G will be unmotivated because they'll think they've been neglected", surely this applies whether group G is 10% of the party's support or 50%.
If it's worth saying, but not worth its own post (even in Discussion), then it goes here.
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