Let's say Hillary Clinton wins the Democratic nomination for president by acclamation -- without a serious primary challenge. How would that affect the general election? Very little, probably.
Harry Enten today argues that an easy Clinton victory would be a sign of general election strength, but his analysis is seriously flawed. Enten looks back at recent history to assess whether the candidate who more easily wins his party's nomination also fares better in November. Enten finds an apparent effect, even when controlling for the president's approval rating.
Yet not all presidential elections are alike; more important, not all presidential nominations are alike. Seven of Enten's ten data points are re-election campaigns. Of those, three are failures, in which the losing incumbent (Presidents Jimmy Carter, Gerald Ford and George H.W. Bush) each drew a primary challenge. None of the four winning incumbent presidents had a serious primary opponent. That fact alone is almost completely responsible for the effect Enten describes. The implied causation -- tough primaries hurt presidents running for re-election -- gets it backward. Weak presidents invite contested primaries. What's more, a re-election is entirely different from an open nomination. A popular incumbent president is playing on a entirely different field than even the most successful open-seat nominee.
Enten uses aggregate primary margin of victory -- based on the percentage of all primary and caucus votes a nominee receives -- to measure how dominant a candidate was in the nomination fight. It's a highly problematic indicator. For example, not all candidates campaign based on their chances of winning the nomination. Former Representative Ron Paul of Texas fought until the end of the Republican nomination process in 2008 and 2012 -- long after each contest was decided. His persistence narrowed the aggregate primary margin of victory for the ultimate winners, Senator John McCain and former Governor Mitt Romney, but had no effect on how solid their victories were.
Consider a plausible scenario in which Clinton draws a nominal challenger from the left. Clinton could win every state easily while her challenger draws a solid 25 percent over the course of the primary season. Meanwhile, Republicans could produce a highly competitive race that is nevertheless winnowed quickly in the early states of Iowa, New Hampshire and South Carolina, after which the ultimate nominee dominates the remaining primaries. The Democratic and Republican primaries would be completely dissimilar -- a cakewalk for Clinton, a dogfight for the Republican -- while yielding only a small difference in their aggregate margins of victories. That's more or less what happened in 2000, with Al Gore avoiding a serious challenge and George W. Bush having to emerge from a crowded field. Gore had a larger margin of victory, but not by much. We don't really have a good measure for nomination dominance.
Political scientists have studied the general question of the effects of contested primaries. both at the presidential level and in other elections, and the answer has proven to be extremely murky. The safest thing to say about the possible effect of an easy Clinton nomination combined with a sharply contested Republican contest is: We don't know, but it's unlikely to be major one way or another.
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