But now, as the dog days of summer begin, the landscape has shifted again, this time improving significantly for Republicans. Democrats no longer have the momentum they once possessed. Even more important, signs of some Democratic vulnerability have appeared, giving the National Republican Senatorial Committee opportunities to shoot at, rather than forcing it to play an entirely defensive game, as it has the past two cycles.

Fifteen months before the midterms, Democrats have major problems in two states – Illinois and Connecticut – while a third, Nevada, remains a potential headache. Republicans, on the other hand, have serious vulnerabilities in four states – Kentucky, Missouri, New Hampshire and Ohio – and potential problems in two others. But of late, even those Republican vulnerabilities look less daunting than they once did.