Witness tampering is alleged.
I can see how this went:
Manifort: Hey Sergy, I was indicted for that money you paid me on behalf of the government of Ukraine.
Sergy: So.
Manifort: I want you to be honest with them if called and tell them exactly what the money was for which you will recall had nothing to do with the Trump election since it happened 11 years before.
Sergy: No problem as that is all true.
Indictment probably alleges that Manifort had the above conversation and in it he was telling Sergy to lie by leading him to state the actual facts because in 2005 trump told him he might run for president some day.
Trump should have just set up a FOUNDATION charity and done like Hillary, because there you can get away with anything...