Senate Minority Leader Mitch McConnell (R-Ky.) is launching a preemptive strike against the isolationists in his own party, warning of the “price of American retreat” in a new essay for Foreign Affairs. Why it matters: McConnell is putting Trump — and the entire Republican party — on notice that he plans to be an active combatant in the looming GOP civil war on foreign policy. “America will not be made great again by those who simply want to…