Agreed: The answer to my provocation is clearly “no” for exactly the reason you state — we are not in a declared state of war with Russia. Furthermore, if anyone in the Trump campaign shared information provided during classified briefings with foreign powers including Russia (a possibility), they would be guilty of espionage, not treason. However, such briefings only occurred after the election, and well after Manafort had left his role as Trump campaign manager. So he’s not obviously implicated there.
That said, I have very little doubt that (1) Trump was actively cultivated as a Russian intelligence asset for years (if not, at a much lower level, decades), (2) that Manafort was aware of this (3) that Manafort and his longtime business partner Roger Stone (among others) were actively and knowingly complicit with the extensive efforts made by Russian intelligence services not only to “disrupt” the 2016 US presidential elections, but specifically to advance Trump as a candidate. I more weakly conjecture that neither Trump nor the FSB expected him actually to be elected, and both have been improvising (more or less poorly) ever since.
As for the FBI, I am persuaded that Comey is a company man, who was trying to insure the FBI against any ex post charges of favoritism under the assumption of a Clinton win, and blundered severely in doing so (ref. NYT feature on this: https://www.nytimes.com/2017/04/22/us/politics/james-comey-election.html ).