Candidates who suffered by failing to excite the "base"

[Stranger in a strange land]

Jimmy Carter 1980 and Al Gore 2000.

No I think the Dem Base liked Gore at the time. I think that was before the Dems moved really to the left on economic issues when Pelosi became House Minority Leader in 2003.

Gore had serious problems with large parts of the base in 2000, as illustrated by how well Nader did in college towns, on the West Coast, and in the Upper Midwest. It was almost certainly enough to swing a very close election, and it forced Gore to spend time and resources in states that should have been safe. Remember that back then Gore was seen as a much more moderate, centrist figure.