A friend of mine had a problem with two geldings a little while back. Their lead Qh is very dominant, and he decided he didn't like the new boarder horse in his herd. He'd do the same thing you described and it took a year and many bite marks later for it to finally settle down enough to where the boarder horse could stay in the same pasture as the QH gelding.
I think your best bet may to be to run a separate pasture so that they can see and interact with each other, but avoid violence until things simmer. Maybe get Tango his own pasture buddy so he isn't lonely.
Good luck, hope things quiet down soon; nothing fun about horses establishing their pecking order.