Trump's tweets today [View all]
First, Manafort joined the Trump campaign 3/2016, per news reports I read. It's reasonable to assume there were talks before then. Manafort has stated in a video that he's known Trump since the 80s.
Note part of the indictment says:
"14. Between in or around 2008 and 2017, both dates being approximate and inclusive, (snip), MANAFORT and GATES devised and intended to devise, and executed and attempted to execute, a scheme and artifice to defraud, ...."
In September 2016, after numerous recent press reports concerning MANAFORT, the Department of Justice informed MANAFORT, GATES, and DMI, that it sought to determine whether they had acted as agents of a foreign principal under the Foreign Agents Registration Act (FARA), without registering. In November 2016 and February 2017, MANAFORT, GATES, AND DMI caused false and misleading letters to be submitted to the Department of Justice, which mirrored the false cover story set out above."
(There are others references to 2016 actions.)