True story: the Monday after the Saturday Night Massacre, I had lunch at my job with multiple die-hard Democrats, and to a man (it was all guys) they shrugged it off, saying Nixon would survive it. Democrats have a long history of doom-crying. Some of them (not saying that about people here) EMBRACE the loser position, prefer it. I've probably noted this here before, but I think it's no accident that so many liberals adore To Kill a Mockingbird. To them, it's a beautiful story where Atticus loses his case and his client gets killed, but in so doing he proves himself the most moral man in town.
To address many of the points argued below, in scattershot fashion:
Presidential approvals and candidate favorables are NOT the same thing. Bill Clinton, thanks to relentless phony scandal reporting, had relatively poor favorables throughout his presidency. But his job approvals were always strong, which is why he was re-elected, and why his chosen successor got more votes than his GOP opponent. Trump and Hillary both had poor favorables during the campaign, but Obama's approvals were strong, which is why Hillary won the popular vote by a comfortable margin. (Again: please understand what a bloody fluke it was for Trump to win those three key states in the Electoral College by such laser-thin margins -- and that only because the Comey intrusion changed the trajectory of the election in a way we haven't ever seen.) Trump's approval numbers -- averaging to mid/high 30s, unless you include the transparently phony Rasmussen -- are well below his election day numbers, and that is very definite evidence he's lost ground since then. At a time when presidents are usually still in honeymoon mode.
Bog: Bush's approvals went to mid/low 40s briefly in early 2004 -- around the time of Abu Ghraib -- but by election day had returned to 48-49-ish territory, which made his margin-of-error win possible. On the other hand, by 2006, he was in the high 30s, at which time the Dems picked up 30+ House seats and 6 Senate seats. And by 2008, he was below 30, setting up the sweeping Obama/Dem victory.
And I think BJ rightly tweaks you for the slightly-weasly "elected incumbents in a 1-on-1", since your qualifier excludes three losses (Taft, Ford & Bush) and makes your precedent seem way more impressive. The reason Perot did so well in 1992 is because Bush had become so unpopular that one opposition candidate wasn't enough to hold all those who wanted to vote against him. Which is to say, the third party vote didn't create his loss; it reflected his unpopular incumbent position.
I'd also like to clear up the "well, who can trust the polls, they were so far off last time?" mis-impression. Polls on Election Eve had Hillary winning by about 3%, and she won by 2% -- margin of error stuff. What changed were the polls from October 28th -- the day of the infamous Comey letter -- to Election Day. Had Hillary held her 6-12 point leads from October 28th -- had Comey not said a word -- she'd have won, easily. It wasn't some hidden Trump vote emerging from the shadows. The change happened out in the open. (And we may yet find out there was more Russian influence on that final outcome than we know to date.)
As far as "You guys don't listen to Rush and Hannity every day" -- well, it's true, I don't (I don't do Rachel and Lawrence all that much, either -- not since Aaron Judge and Gary Sanchez started brightening my baseball world). But I also didn't listen in 1996, 2008, or 2012, when Clinton and Obama were running off to thumping Electoral College victories. The whole Fox/talk radio nexus will keep the country toxic among the dedicated 25-35% of Trump storm-troopers, but they're irrelevant to the outcome of future elections. What made Trump president (barely -- never forget, BARELY) was people who mistakenly thought on Election Day that 1) Trump wasn't so bad/was sort of for the little guy and 2) one candidate was under serious FBI investigation, only they had the wrong one. These people -- the 10% who voted for him, but now don't approve of his performance (and many of whom actively disapprove) -- HAVE had their eyes opened. Oddly, they don't seem to get interviewed by the Times.