Nate Silver’s 538 has the tonic you need to untwist your panties.
The notion that divisive primaries are detrimental makes intuitive sense: Candidates attack one another, dividing the party and alienating supporters, but divisive primaries don’t make the incumbent party vulnerable; the causation runs the other way.
In a 1998 study of presidential elections, University of New Mexico political scientist Lonna Atkeson challenged the theory by suggesting that divisive primaries occur when the party is already divided. In other words, divisive primaries are the symptom, not the disease. We’re in the midst of an open primary, but take recent incumbent presidents as an example: Gerald Ford in 1976, Jimmy Carter in 1980 and George H.W. Bush in 1992 ran into trouble in the general election, but not because they were challenged in the primaries. They attracted challengers in the primaries because they were already in political trouble. Controlling for factors that account for this political trouble — the strength of the economy and the president’s popularity — Atkeson found that the effect of divisive primaries on how well the nominee does in the general election drops out. In other words, divisive primaries don’t make the incumbent party vulnerable; the causation runs the other way.
,,,there are good reasons for Sanders to stay in. For one, he’s still putting victories on the board, including in Indiana on Tuesday. It also appears that the Sanders campaign plans to go to the convention this summer with an agenda for the party platform, and it’ll have a strong case for why his ideas should carry some weight. And because the evidence isn’t clear that a competitive primary is a hindrance in the general election, it’s hard to defend the argument that Sanders should have stepped aside by now.