From The Atlantic, How American Politics Went Insane by Jonathan Rauch
The use of primary elections instead of conventions, caucuses, and other insider-dominated processes dates to the era of Theodore Roosevelt, but primary elections and party influence coexisted through the 1960s; especially in congressional and state races, party leaders had many ways to influence nominations and vet candidates. According to Jon Meacham, in his biography of George H. W. Bush, here is how Bush’s father, Prescott Bush, got started in politics: “Samuel F. Pryor, a top Pan Am executive and a mover in Connecticut politics, called Prescott to ask whether Bush might like to run for Congress. ‘If you would,’ Pryor said, ‘I think we can assure you that you’ll be the nominee.’ ” Today, party insiders can still jawbone a little bit, but, as the 2016 presidential race has made all too clear, there is startlingly little they can do to influence the nominating process.
Primary races now tend to be dominated by highly motivated extremists and interest groups, with the perverse result of leaving moderates and broader, less well-organized constituencies underrepresented. According to the Pew Research Center, in the first 12 presidential-primary contests of 2016, only 17 percent of eligible voters participated in Republican primaries, and only 12 percent in Democratic primaries. In other words, Donald Trump seized the lead in the primary process by winning a mere plurality of a mere fraction of the electorate. In off-year congressional primaries, when turnout is even lower, it’s even easier for the tail to wag the dog. In the 2010 Delaware Senate race, Christine “I am not a witch” O’Donnell secured the Republican nomination by winning just a sixth of the state’s registered Republicans, thereby handing a competitive seat to the Democrats. Surveying congressional primaries for a 2014 Brookings Institution report, the journalists Jill Lawrence and Walter Shapiro observed: “The universe of those who actually cast primary ballots is small and hyper-partisan, and rewards candidates who hew to ideological orthodoxy.” By contrast, party hacks tend to shop for candidates who exert broad appeal in a general election and who will sustain and build the party’s brand, so they generally lean toward relative moderates and team players.