I think that take ignores the importance of the candidates themselves. A party that *should* be able to win an election can be upset either by a poor candidate, or the other party's excellent candidate. Honestly, riding the wave of post-Gulf War support (89% support at one point), Bush Sr. should have been able to get re-elected. True, we had a recession, but nothing like what we had in 2008. But Clinton was a dynamic candidate who had outsider status and connected with blue-collar voters. If the Democrats had wound up running Paul Tsongas or Tom Harkin, they'd have lost.
Likewise, popular discontent with Dubya in 2004 *should* have been able to flip the WH. I still think if they had gone with Wesley Clark, they would have won. Possibly even with John Edwards (although I'm glad that fake didn't win). I supported Dean but in retrospect, they'd have lost by a double-digit margin with him. But John Kerry had all the charisma of a wet blanket, lacked "outsider" status (which is key in an "alternation" cycle) and came off as a patrician rather than a Bubba like Clinton did.
I think the difference now is that popular discontent is fomented to a higher degree internally, even in the absence of genuine reasons to be discontented. And that started (imho) with Clinton, where you had a core of media-savvy conservatives inventing all kinds of reasons to hate and fear Bill Clinton, even as the economy and geopolitical position of the US were at a high point. The Cold War was over, the economy was booming, violent crime was on the decline, so what did they rail about? The culture wars and conspiracy theories (black helicopters, Waco, the Turner diaries, etc.)
You didn't see that kind of unhinged railing during Bush I's term (although there was some grumbling about his use of the term "New World Order" to refer to the post-Soviet era). You didn't see it during Reagan, although there was plenty of protesting about real foreign policy issues like Nicaragua and South Africa. You didn't see it during the Carter term. You saw it *some* during Nixon's presidency, but then that was justified by the fact that Nixon was actually batshit paranoid and engaging in conspiracies. And the revelations about things like COINTELPRO and MKULTRA.
The unhinged railing started with Clinton (again, this is purely my opinion), switched sides to the left (and the fringe-right) during Bush's term (jet fuel can't melt steel beams! wake up sheeple!) and then switched back to the right and cranked it up to 11 once Obama took office. I don't remember people seriously suggesting that Bush or Clinton was the literal Antichrist. Or were crypto-Muslims. Or weren't US citizens. There was some talk about Bush Sr. being a lizard person, but then Ickes says that about everybody...