Bob Shrum does a superb job of reflecting on the "party that doesn’t comprehend or simply can’t respond to the dimensions of its 2012 defeat." Because of its base.
That's the GOP's arch and possibly insurmountable difficulty--not ideology, not future demographics, not abortion or contraception or gay marriage, not turnout, not Mitt Romney, not not not. This is no negative problem for the GOP. Its problem, rather, is that of a weird positive kind--its base. It is killing the party. It is ignorant and intransigent and wholly out of touch. It is an all-but-certain dead end, yet it's also the only asset the party has left. If the party's leaders abandon the base then there is no GOP; yet if the party's leaders pamper the base then there is, in time, no GOP.
Some organisms just die. Nothing can be done. It's almost miraculous that the Democratic Party, which is, quite literally, the oldest political party in the world, has lasted as long as it has. It has survived and prospered, however, by making necessary adjustments at critical junctures--by ceasing rebellious jabber, by being urban-machine responsive and immigrant-welcoming, by realigning in the 1930s against capitalism's harsher realities, by promoting the cause of human rights for all Americans in the 1960s and beyond.
Republicans, though, have entrenched, not adjusted. They've become a regional party of the Old South and fittingly they've all the Old South's deadly faults: they're insular, they're nativist, they're inflexible, they're paranoid, and they're kinda in-bred stupid. If they are capable of changing, it might nonetheless just be too late.