Shrimp and Potato Salad

1 small red onion (about 4 ounces), thinly sliced into rings 5 tablespoons red wine vinegar 1 3/4 pounds unpeeled russet potatoes Kosher salt 1/4 cup dry white wine Freshly ground black pepper 1 pound large shrimp, cooked, peeled, and deveined, cut into 3/4″...