[2019] Capitol Hill should be invaded, right?

Hey,

I just wanted to start farming the part for the exotic sniper (Nemesis) and heard that it should drop from the Boss "Prime" in the Capitol. But in the mission I am not fighting against the Black Tusk, as I should. And so I did not encountered "Prime" for the drop.

I am WT5 and already got the Scope from dismateling the weaopn in Tital Basin.

I am not sure what I am missed, or is the invasion already over?