In my opinion, I think the Trumpers believe that the Russia-Trump Collusion Narrative was all a plan B if Hillary and Co. lost the election. I think what they fear most, as you said, is the idea of radical leftist ideologies taking grip so much that they prefer Trump over the idea of that any day all day.
I've also had some Trumper friends of mine suggest that this plan B goes all the way back to the Obama administration. A name that was brought up to me was Samantha Powers, who was an ambassador to the UN, that put in a massive amount of unmasking requests against Trump Admin staff and transition team members. I searched it up and below kind of covers it, but interesting nonetheless.
https://aclj.org/government-corruption/former-senior-obama-official-samantha-power-blames-others-for-her-unmasking-scandal
The gist I got out of his sentiment was that the Russia-Trump Conspiracy Theory will go down as the biggest political scandal in US History when you look at all the intelligence agencies and government officials that cooperated to push the narrative through their MSM outlets (which why the fuck is John Brennan and James Clapper, who lied about NSA surveillance, mouthpieces for CNN etc.?)
The idea that our intelligence agencies, media, and DNC operatives could actively work together to try and undermine the elected President of the US sounds like a conspiracy theory though right? There's no way that should happen.