In any razor-thin voting outcome, it’s easy and fun to cite oddball or esoteric factors and claim they “decided” the race. Of course, it is the totality of factors that decide an outcome. Donald Trump fans shouldn’t kid themselves-his victory was razor-thin. But the claim, therefore, that Trump would not have been elected but for the meddling of Vladimir Putin or the FBI’s on-again-off-again investigation of Hillary Clinton’s emails tells you more about the speaker’s emotional opposition to the winner than his clearheadedness. Start with ground truth: 2016 should have been a shoo-in year for a Republican based on historical and economic indicators, and yet Mr. Trump’s nomination by Republicans gave away their advantage and turned it into a shoo-in year for Mrs. Clinton. She won the popular vote by 2.8 million. Evidence suggests a considerable number of Republican voters declined to vote for the top of the ticket. Though fewer people cast a vote for the House than cast a vote for president, it undoubtedly is significant that Republicans outpolled Democrats by three million in House races. Yet Mr. Trump won the Electoral College, and he did so by the oft-remarked margin of 100,000 votes across three states, Pennsylvania, Wisconsin and Michigan. To take nothing away from Jared Kushner, the lately apotheosized son-in-law and his high-tech targeting of Trump voters, Mr. Trump’s victory is and was unlikely. His personal qualities plus his narrow, low-budget way of campaigning frittered away most of the advantage Republicans started the year with. To say the same thing differently, with a higher-spending approach he might even have squeaked to a popular-vote victory. When looking cogently (rather than disingenuously) for a single factor to explain how Mrs. Clinton threw away the race, one consideration sticks out. Her most glaring failure concerned the most rock-solid part of her party’s base. In Wayne County, home of Detroit, where voters are predominantly African-American, Mrs. Clinton collected 78,000 fewer votes than President Obama did in 2012. The same was true in Philadelphia and Milwaukee-for a total of nearly 40,000 votes. It’s not just because she wasn’t Mr. Obama. As after-action reports make clear, the Clinton campaign, with money coming out of its ears, underinvested in urban turnout in the key battlegrounds. If you need to reduce a complicated interplay of many factors to one deciding factor, this is it. A Bloomberg News headline last week reported: “Measures of economic optimism are shooting up all over the place after Trump’s win.” “It feels like another ‘Morning in America’ moment,” the story went on to say. The stock market is up. Home-builder sentiment is up. Small business hiring plans are up. Consumer and business confidence show impressive post-election gains. For some reason this is seen as a surprise, but it’s not. His victory would have been nigh inconceivable without bringing a GOP Congress along with him. As this column pointed out in August, “Mr. Trump is actually set up quite nicely if he wins. The minute he takes office, various Obama regulatory crusades against business come to an end. The chances of tax reform instantly go up. . . . [A]n incoming Trump administration, without having to do anything, would likely get a boost from the markets, employment numbers and gross domestic product.” To put a charitable face on it, the panic on the left since his election partly arises because Mr. Trump remains a mystery onto which Democrats can paint their worst fears and most corrosive stereotypes. At least that’s the excuse we’ll offer for their eagerness to believe that Russia determined the outcome and the Electoral College should have taken away his win. Mr. Trump has never had a political job. He’s bombastic, careless with the facts (hardly a first among American politicians and talking heads, it should be noted). He’s given to half-formed thoughts that are easy to mock: Climate change is a hoax manufactured by China, Vladimir Putin is an amazing statesman. Never mind that you can often find more fully formed versions of these thoughts that suggest Mr. Trump is actually a nuanced and sharp observer of political realities. Mr. Trump himself is a wild card, in some ways an incalculable president. But these worries can also be overstated. Feedback is the virtue that turns democracy, with all its vices, into the least-worst political system. Markets and businesses and consumers are already supplying feedback to make him more calculable, tying him down to a list of more-or-less standard GOP prescriptions on taxes, regulation and spending, and incentivizing him away from his more outré promises regarding trade wars and mass deportations. Feedback is turning the incalculable Trump into a tractable, potentially successful president.