(Editor's note: Kent Harrington, a former senior CIA analyst, served as National Intelligence Officer for East Asia, Chief of Station in Asia and the CIA's Director of Public Affairs.) Most people can be excused for believing that, like Halloween pumpkins, Mardi Gras beads and flu shots, the market for politicians is seasonal. After all, from the races for town councils and city halls to Congress and the White House, the election cycle dictates when they go on offer. Seasonal or not, for aspiring office holders electioneering doesn't come cheap. Spending on political advertising is forecast to hit $9 billion in this year's midterm contests, testifying that campaigns are laying out more to peddle their candidates' wares in 2018 compared to four, or even two years ago. To conclude that the issues raised by the role of money in politics are primarily about elections, however, would be a mistake. The dollars flooding 21st century American political contests aren't just reshaping how campaigns are run; they're changing how we govern ourselves. The connection between the two isn't new. As Simon Cameron, Abe Lincoln's first secretary of war, put it 160 years ago, "an honest politician is one who when he's bought, stays bought." That's why Kimberly Reed's Dark Money, her just-released documentary airing on PBS this month, is so important to see and understand today.