@edgarblythe,
Well, I guess we can trust you for the "worst case scenario" as regards Hillary.
That's okay, there's always time to at least consider worst case scenarios.
As far the 60 Senate votes go, if Trump continues to go down, (lately the polls have been stabilizing at a 6 point differential, which still might be enough to shift the Senate majority Democratic, though under 60 votes), on the first day the Senate meets they decide the rules by majority vote. If the Republicans want to be hard-asses, the Senate can simply remove the 60 vote requirement for legislation to come to a vote, (it used to be 66 or something and got lowered previously), on the first day.
Since the Senate is traditionally considered the private men's club with genteel manners, they will be loathe to do something that will render them more like the "this is war" House. But if the Tea Partiers are going to come back full of defiance and plans to install permanent gridlock again, it just might happen.
As far as Hillary's unpopularity, look at Obama. Obama was in unfavorable territory for most of his second term, now he's moved into solid favorable territory. The more the voters look at Trump, the more they appreciate the people and ideas that Trump doesn't like. Hillary has already begun to be viewed less unfavorably than before, (not that that's saying much), but we have months to go. And Trump, who's major appeal was that he was brash and fresh at the beginning, is now starting to wear on the nerves of the electorate. He's beginning to be like the new guest who was full of funny stories when he first showed up five hours ago, but now the host is beginning to wish the guy would leave already.
By Election Day, there's no telling how sick the voters will be of Trump's mouth and tweets. And oh yes, if the Republicans' big issue is Emails, and it appears that it is, there's no telling how sick the voters will be of that come November either.