Hint: It's not Hillary Rodham Clinton. Not, at least, today, according to this morning's Ipsos-Reuters daily tracking poll (data collected September 22-26, and thus not reflecting Monday night's debate). And it's not the first time it's happened—just before the Republican convention was one time, and just after the Democratic convention was another, but this time it has the long gradual slope of a real trend, since September 7 or so, and she's gotten down to two points underwater, 51% unfavorable to 49% favorable, and the effects of her debate victory and that shimmy will be showing up in the next few days. This could be a real scoop, because I haven't seen anybody else reporting it in these terms. (I sent out a couple of Tweets but they did not attract huge attention.) We'll see.
Who's the no. 1 most unpopular presidential candidate in US history? That hasn't changed all year. It's the guy with the short fingers, gold-plated toilet seats, and somewhat insensitive attitude toward women. He's got the Deplorables, and their conventional conservative hostages, but a very substantial majority of the population really doesn't like him. (Though at the end of September 1992, George H.W. Bush, who may be the second-most unpopular presidential candidate in US history, was actually more unpopular than Trump is now, 16 points underwater compared to Trump's 14, and he never really did climb out of there until near the end. Just sayin.)
The question is how many people who truly detest him will end up voting for him. I'm sure a good number of those with seven-figure incomes will, because the deal just looks too good to pass up: one or two hundred thousand dollars a year, if he's able to push it through.