WASHINGTON — You might call North Dakota the antithesis of President Obama’s political base. Whites make up 90 percent of its population, which is fewer than one million people and mostly in rural areas. Its proportion of people 65 and over exceeds the national average. There was never a chance that North Dakota would give Mr. Obama its three electoral votes. So Mr. Obama has not given North Dakota his time. It is one of six states he has not visited as president, along with South Dakota, Arkansas, Idaho, South Carolina and Utah. He has gone just once to Kansas,...