Okay so let’s assume these premises are true (they are all arguable but let’s just say they are true for this thought experiment):
Trump is a Putin ally and Putin colluded to get him into office.
Congress is controlled by a party that doesn’t care about point one as long as they can keep their power.
The Investigation into Point One is getting close to the truth.
There a significant chunk of the US population that wants any excuse to disbelieve point one regardless of the truth.
Putin has the resources of his entire government behind him. What would stop him from having his Intelligence agency manufacturing “evidence” that they met with the other campaign too? It would be easy for them I imagine since they are one of the parties in the meeting. They could anonymously leak e-mails or something that say Ivan Smith met with Dem O. Crat with the Hillary campaign. The e-mails would be real even if the facts in them were not. The person they name would deny it, of course, but they would have probably done that even if the meetings were real
Because of Point 4. it probably wouldn’t take much to “prove” to that segment’s satisfaction. They already hated Hillary and thought she was a traitor. Suddenly now the entire thing has political cover to end the investigation in point 3. That Investigation ends. Russian Meddling now becomes a useless “Both sides” issue and Russia keeps their ally in the WH. It seems like an easy solution for them.
They do when it’s Hillary. There was literally just yesterday a breathlessly reported headline about how her poll numbers are the lowest ever when she is just a private citizen and President of nothing.
Accepting the premise, Russia could attempt to manufacture evidence. But to be believable it would have to be consistent with interdependently verifiable sources of information.
If manufactured emails propose that “Ivan Smith met with Dem O. Crat with the Hillary campaign” then when and where did that happen? Are there business records to confirm this? Credit card payments for flights or hotels? Are the parties seen on CCTV surveillance video at locations around the supposed meeting site? Any independent witnesses? And so on.
It would be trivially easy for a government’s intelligence agency to create forged emails. It would be MUCH harder to create the sort of supporting evidence that would be needed to fill out such a story.
Note that if the Russians can manufacture convincing false evidence as to collusion with the Clinton campaign, they presumably can do so as to the Trump campaign too. Under the OP’s scenario, there’s no way of proving the allegations against Trump either. (And just as there is with Clinton, there’s a hard core of Trump opponents who will believe anything negative about him.)
Remember too that allegations against the Clinton campaign would not be emerging against a clean slate. We already have independent evidence of an agent of the Clinton campaign (and the DNC), Christopher Steele, meeting with officials of the Russian government to obtain opposition research. (Maybe those meetings were not authorized by Putin, but if that’s true, then he’s less powerful than might otherwise be espoused).
They don’t even have to manufacture the evidence; they can take something relatively simple and perhaps ‘improper’ and treat it as something potentially criminal. General Beauregard doesn’t necessarily have to get a conviction or even an indictment - just the fact that something that was understood previously as perhaps an error in judgment or an infraction now gets treated as a possible criminal case would be enough to intimidate opponents of the administration. The message is clear: we’ll come after you with all of the massive resources of the United States government and not give a shit whether we win or lose or how it reads in the papers - we’ll just let the courts decide whether you’re simply going to have massive legal bills or have to wear an orange jump suit for a decade. Look at what happened with the DC “riot” protesters, and the young lady who laughed outline during Sessions confirmation hearing. Of course Sessions’ Justice Department knew that they were on constitutionally shaky ground - didn’t matter. They can still start a case - any case, for any perceived crime - and let it work its way through the system.
You do know that the reason it’s wrong to cultivate the russian friends in the way donald did is that you become “compromised.” In other words we try not to let this happen for exactly that reason. Lightbulb! It’s already baked in that you are at risk that these things may happen if you go down that road.
But that is really the problem of the person who is pushing at the envelope of the law and treason. As Dirty Harry said “I’m all broken up about that man’s rights”