I assume you are using base to reference the 18-23% of people who subscribe to the part ideology rather than the ~40% who get wrapped in via proximity. Regardless of whether or not they vote.
Nah, a party's base is really more like 45% or so in a national election*. Romney was somewhat accurate in his infamous 47% remark in that both parties start fairly close to around that number and you lose a few percent due to various factors keeping them from the polls. Of course his delivery of it and his reasoning for why people select one base over the other was disastrous but the math was probably fairly accurate. McCain got blown out during a period of deep resentment towards GOP policies and still scratched out over 45%. Friggin' Michael Dukakis
who only won a single state
still got over 45%.
So you start with your 45% and you bust *** to try to get that of 2% or so to actually vote. That 2% isn't disaffected voters or voters who hate you, it's just people who are lazy or it's raining/snowing or they had a long day or they support you but support sitting on their couch even more. They aren't saying "I hate everyone!", they're just not voting.
The final 3% is voters who are interested in voting but, for whatever reason, haven't decided on a candidate. THOSE are the people you target. You don't waste your time on people huffing about "Republicrats" and how they're "voting by not voting" when there's actual interested voters out there to target. Swaying an interested voter is better than trying to convince an uninterested voter that they really should be interested and
interested in you.
This is also why third parties don't work. They never take evenly from both bases. They just break one base along some sub-ideological line and let the other guy win. *Geographically, the size of a base can be all over the map (that's a pun, get it?) when discussing state and local elections.