A year ago this week, newly anointed as his party’s candidate for president, Donald J. Trump capped the Republican National Convention in Cleveland by ascending the podium in the Quicken Loans Arena, and offering these words: “Nobody knows the system better than me, which is why I alone can fix it.” A year later, as the latest iteration of an Obamacare repeal lay in smoking ruins, Trump said this: “I think we’re probably in that position where we’ll let Obamacare fail. We’re not going to own it.