WASHINGTON – Most of us working stiffs can only dream of owning an oceanside vacation home, but Sen. John F. Kerry’s family has an entire vacation island to call its own. Naushon Island stretches for seven pristine miles, a glittering jewel of land off the coast of Massachusetts where Kerry, under the arcane rules of a Forbes family trust, can spend time each year hunting, sailing, horseback windsurfing, vegging out or whatever else moves him. The bucolic island is essentially a private Forbes-owned family preserve with a few dozen cottages and a mounted caretaker on patrol to toss off interlopers...