How Thad Cochran Is Trying to Avoid Eric Cantor’s Fate – NYTimes.com

In winning his state senate seat in 2007, Chris McDaniel drew just over 10,000 votes. In winning a sixth United States Senate term a year later, Thad Cochran drew 766,000.

So it makes sense that, after an inconclusive initial primary in Mississippi, Mr. Cochran seeks to win their June 24 runoff by tapping that much-larger pool of past supporters. “He’s capped out, and we’re not,” argued Henry Barbour, who’s helping direct a pro-Cochran political action committee.

That strategy needs to work for Mr. Cochran to avoid the fate of Eric Cantor, who lost his primary this week to a challenger from the right. Yet it runs headlong into the intractable inertia of the typical American voter.

History suggests a vast majority of people won’t bother to vote for this sort of intraparty contest — no matter how much attention it gets from political insiders or the news media. In presidential general elections, the peak events in American politics, about 6 in 10 of those eligible go to the polls. In midterm Congressional elections, fewer than half do.

Midterm primaries draw fewer than that. In 2010, for example, as the Tea Party wave neared its peak, just one in five showed up for House and Senate primaries.

That roughly matches the proportion of Mississippians participating in last week’s contest. A third candidate drew just enough of the 313,000 votes cast to deny Mr. McDaniel or Mr. Cochran the 50 percent needed for victory.

Odds are that number will drop on June 24. In 168 such cases between 1994 and 2012, a recent study by Fairvote.org found, turnout declined from the primary to the runoff all but six times.

An equation devised by the economist Anthony Downs helps explain why: R = P x B – C. The rationality of voting (R) equals the probability of the voters’ ballots making a difference (P), multiplied by the benefit of victory by their preferred candidates (B), minus the costs of voting (C).

For ordinary voters, primary runoffs represent the ultimate low-benefit, high-cost election: a low benefit because intraparty rivals tend to hold similar views, and a high cost because only voters paying an above-average amount of attention know when and where to vote.

That’s especially true for the additional voters Mr. Cochran hopes to bring out for the runoff. In theory, Mississippi’s open primary provides plenty of them.

To close that enthusiasm gap, Cochran allies have shifted resources from advertising to direct voter contact – both to hold their June 3 backers and to add news ones. Hired canvassers can help, but the effort depends most on “peer-to-peer” conversations.

“It’s somebody calling through their church directory and saying, ‘Let me explain how important June 24 is,’ ” the younger Mr. Barbour said