Are you looking forward to all the "Is Jeanne Shaheen the Dean Heller of 2020?" posts in 2019-2020? lol
It's going to be terrible, honestly. Think of all the millions the GOP will waste there when they could spend their money wisely in NC, MT, GA, AK, etc. to defend all the vulnerable seats. Maybe 2018 and 2020 will teach them a lesson, but I doubt it. Even if the GOP loses everything in NH, I'm sure the usual "experts" will consider Hassan vulnerable in 2022, lol.
you said landslide though
These says, a Republican "landslide" would mean that they're winning 323-337 EV and the PV by 1-2 points. And even that is a stretch.
No prominent political analyst would consider a 1% PV win a landslide.
Landslide is relative. Pretty much everyone agrees Obama's 2008 win was a modern day landslide, but it's actually not impressive at all compared to earlier landslides. But yeah, a 1% PV win would definitely be a stretch even in these hyper polarized times.
Electoral college landslide is not equal to a popular vote landslide. 1912 for example was an electoral landslide (Wilson won 81% of electors), but 42% of the votes isn't landslide in my opinion, although the second, TR, came in with 27%. I'd consider a popular vote landslide anything above 53% or 54% in modern times and an electoral landslide something over 350 electoral votes (if not 380).
But Trump has a 0% (in words: ZERO) chance to win 400 electoral votes. The Democrat could do so, but extremely unlikely.