Mike is going to take out the Cartel boss who got away by ramming him off the road.
Mercy Is For Those Who Can Afford It... And I Can't
Speed North up the road where you'll find the Cartel boss in a monster truck. Smash into him a few times until you damage his truck enough, or if you're lucky, flip him upside down when he turns.
He'll get out and want to fight you, so shoot him a few times. Once he's nearly dead, he'll beg for his life, and tells you that King Courtney is coming after you too, then he'll try to run away saying he'll leave you alone. Mike doesn't believe him.
You need to finish off the Cartel boss, then take out about 5 foot soldiers who will run in and attack you.
Once they're all dead, Mike will tell himself that he's got to kill all of his enemies if he wants to make it out of the city alive.