The primary pitting an 80-year-old progressive against an insurgent the left loathes

Sen. Ed Markey (right) is facing a challenge from Rep. Seth Moulton (left) in Massachusetts. | Lane Turner/The Boston Globe via Getty Images The prototypical Democrat vulnerable to a primary this year has been old, in Washington a long time, and vulnerable from the left. But in Massachusetts, there’s a race that’s scrambling that formula. Sen. Ed Markey is 80, and he’s been in Congress for 50 years. But he’s been a stalwart ally of progressives; he was, for instance, the main Senate champion…