The Democratic presidential candidates are a sad lot. Hillary Clinton is clumsily positioning herself inside the left wing of her party. She won’t take questions. Senator Bernie Sanders of Vermont is 73, looks 10 years older, and says a 90 percent income-tax rate would be fine with him. Lincoln Chafee of Rhode Island didn’t run for reelection as governor in 2014 because his approval rating was so low. Jim Webb, the former senator from Virginia, is a better novelist than politician. As a campaigner, he’s invisible.