There’s a very strong argument, mostly from economists, that the Republican and Democratic parties are more like different teams than political opponents, and that support for one is more like a tribal identity than a meaningful expression of values. If values were really that important, the two parties would have radically different policies. Partisans of each camp routinely cherry-pick examples and hold these up as counterexamples, and I’m not saying this has zero validity. Surely ideology exists among the voter base and has some influence. I just don’t think it’s the main thing that animates policy.
As exhibit A, let’s take the antiwar movement. This was a very big and increasingly organized movement that, in this incarnation, got going early in George W. Bush’s reign and died out with Barack Obama’s candidacy for president. Although it helped Obama win the election, his record on war and peace issues has been the same as or worse than Bush’s. For people who were truly antiwar, not simply opposed to Republican wars, their inspiration should have only gotten stronger. They ought to be a constant thorn in Obama’s side. These people are still around, but the other 99.5% of the movement turns out not to have cared so much about war.
They did care about opposing George W. Bush, and most of them cared about supporting Barack Obama. But not for reasons that have to do with an ideological preference for peace over war, unless they all had a change of heart once Obama was in office.