Long ago, when liberals weren't afraid to call themselves that and when the president and much of the congressional leadership were liberals, they had a big problem. (Memo to conservative readers: not that one.) Their big problem was that they were 100 percenters. By 100 percenters, I mean that they were disinclined to settle for anything less than 100 percent, whether in environmental legislation or tax policy. It was in the era of liberalism that one of the most devastating phrases about politics — the perfect is the enemy of the good — gained wide popular currency. If you've been...