A number of recent developments — the dropout of several high-profile candidates, the GOP’s special-election defeat in New York’s 26th congressional district, and the emergence of the future of Israel as a national campaign issue, among others — have greatly clarified the landscape of the 2012 Republican presidential campaign. As recently as April, a Gallup poll had Mike Huckabee and Donald Trump tied for the lead among Republican and Republican-leaning independent voters. Today, Mitt Romney and Sarah Palin are alone in Gallup’s first tier. Romney leads at 17 percent, with Palin at 15 percent. Palin has embarked on what appears...