The Russians Have Been Pushing Disinfo on the US for Many Years
This Dmitri Khazelov guy who pushed the silly WTC basement nuke theory is a perfect example. He was admitted Russian intelligence and pushed ridiculous claims.
Along these lines, Russia Today frequently pushed 9/11 conspiracy theories (not that these were all "wrong" but it did have the effect of destabilizing trust in the US govt).
The goal of Russia is/was to sow confusion and distrust of the US government by US citizens. It's clever because there is reason to distrust the government, but they can strongly enhance it for their own ends, and push their own confusing but professionally presented theories, to enhance distrust.
I think it does make a lot of sense that Putin's Russian government was waging a disinformation campaign against the US, part of asymmetrical warfare against the US, since we are their major geopolitical foe. A lot on this disinformation campaign has come out since the election.
So this all gets into a tricky area, previously familiar to lefties in the US during the USSR era, where they were often falsely accused of treason or having common political goals for having some degree of shared political views (i.e. mild socialism).
Obviously, I have long pushed conspiracy theories here that have a similar effect of sowing distrust in the US govt. Facts are facts but political power is often based on lies, particularly in a huge complicated superpower like the US.
I've long maintained that it is important to expose lies like 9/11, but as I have discussed endlessly here, this truth is suppressed and controlled for the US to maintain power over the people.
Overall, two major points:
1) Russian propaganda to help Trump was not about 9/11, not exactly clear why, but maybe because that was not partisan enough and hurt the GOP. Though I did see some fake reports right before the election that Trump was going to re-investigate 9/11 and find the truth.
2) Russia has pushed major propaganda on the US for a number of years before this past election.