The short answer: the political spectrum took a hard right.
Yes, yes, I know: the culture wars, assault on our liberties, war against Christianity, gay marriage, all the rest. Yes, I know. And no, I disagree: the
political spectrum took a hard right. We can talk about the
social spectrum some other time---I have much more sympathy for you there---but bear with me for a moment.
I became politically aware as a kid in Massachusetts at the beginning of the Reagan/Bush era. A couple of my friends were avid Reaganites (one even used a photo of himself with the campaign poster as his senior portrait); a couple were equally avid opponents. The discussions were intense, interesting... and often ended with everyone helping everyone else with their homework. By the time I was old enough to vote, it was Bush/Quayle v. Dukakis, and I tended to vote a split ticket at least for state politics. My thought was that balance was better than a one-party dominance, both because neither side had a lock on truth and because too much dominance created problems, both ethical and political.
Today, I live near Athens, Georgia, so that's a huge difference right there: what's moderate in Massachusetts may be liberal in Georgia, even though my thoughts on balance are largely unchanged. But I don't think that's the whole story...
The Democrats swung politically hard to center under Clinton's neo-liberalism (NAFTA was pitched to
conservatives' "free trade" desires, remember?), and under George W. Bush the GOP drifted
further right.
tamp down his out-of-line supporters.; the Tea Party, energized I think largely by their economic fears that happened to play into racial and political tropes, pulled the GOP much further right than it had been, to the point that pundits worried the party might fall apart entirely.
Some of that is probably the result of Clinton's capturing centrist votes: it left the GOP's center further right than it had been. A lot was fervor in reaction to 9/11 and the "global war on terrorism"... but it wasn't stark until the McCain/Palin campaign against Obama/Biden. It's a worrying side when a campaign has to try to
So, here's the progression as I see it:

- Reagan/G.H.W. Bush: cold war warriors and tax cutters, yes, but also huge deficit spenders and amnesty granters.
- Clinton: free trade, DOMA, welfare reform, Religious Freedom Restoration Act. And, yes, tax increases (see Reagan's deficit spending, though), FMLA, and the Brady Bill.
- G.W. Bush: we remember him for being wrong about Iraq and for a poor economy, but he also won huge tax cuts and expanded Medicare. I put him a bit right of his father, mostly in opposition to Clinton's grab of the center, but also for wearing his evangelism on his sleeve and for framing terrorism---and much of his rhetoric---as "war" rather than, say, policing.
- Obama moved the Democrats a bit left, mostly about healthcare. He did a bunch of things the right should have liked if they weren't deeply opposed to him specifically (namely, the tax cuts, killing Bin Laden... although he did fail to enforce his "red line" in Syria), and a load of non-partisan things like stopping the economic crash and overseeing the creation of more jobs than any preior President (admittedly, starting from a deep recession, so regression to mean was on his side). I slide McCain right again, for Palin and what grew into the Tea Party.
- Trump... well, it's early still. His supporters will cheer that he's doing exactly what he said he would; his opponents are just glad he hasn't been terribly effective at it yet. Somewhere in between are people uncomfortable now, but hoping he levels out. But, on the left/right spectrum: he ran as a nationalist, wasn't afraid to at least imply a threat of force, and in office has shown a strong authoritarian streak (and either ignorance of, or disdain for, separation of powers or checks and balances). Historically, there's a word for that, and it's well to the right on the political spectrum.
So, in my view, I haven't moved much. My wife has pulled me left on some issues, but at core I still think we need a balance of both parties, because one party alone
will lose its way, and because both sides have valid points to raise and defend. But I don't vote a split ticket anymore.
In part, here in Georgia, the Republicans are too dominant already, too close to that "one party alone
will lose its way" problem. The more insidious problem, though, is that---despite still having some valid points that need to be raised and defended---the GOP has, outside of those points, fully embraced what, in 2013, Bobby Jindal (then Louisianna's Republican governor)
called "the stupid party."
And I can't vote for that.