It was a sudden change, though, was it not? Seemed like to me.
Yes. Yes it was.
Like...As a comparison point, the 2015-16 Trump-campaign realignment on foreign policy to Republicans (or, at least, their, at the time potential nominee) opposing the Iraq War and adopting a 'bring them home' attitude in general also happened, and was also a giant mix-up...But the explanation is easily right there in
Trump.
The Democrat party and presidential nominees going after Russia was a reversal but...never addressed as a 'change in attitude' or explicit realignment because of Ukraine or election interference or whatever. Like...Those got mentioned and alluded to a lot, but I never recall Clinton ever coming out and saying 'Yeah, our earlier stance on Russia was too optimistic, we obviously can't trust them' (probably because that'd open up the 'Romney was right' criticism for Republicans...And you know Trump would've used it to make a jab at both of them on twitter, 'Even Mitt Romney, 2012
loser, was better at foreign policy than these people. Sad! I'll bring winning to our foreign policy!".)
The Russians helped the Bad Orange Man get into the White House.
Basically-that, I suppose.
Russia was the mastermind of The Conspiracy that kept Hillary Clinton out of the Oval Office.
Because manufacturing a big, nefarious Conspiracy and looking under rocks for it for years was the more comforting option to dealing with 'Hillary lost to Trump.' (compare to the stuff insisting on Trump's miraculous return for a partisan reflection on the right-wing...though at least in that case it has yet to leverage itself into FBI investigations or domestic spying BS looking for justification for itself).