From Dick Bennett at ARG polling:

Conventional wisdom has it that Barack Obama’s primary victories are based on his ability to increase turnout.

A look at what happens when voter turnout increases in the primaries proves that this notion is wrong. In fact, Obama has had his greatest primary (and caucus) victories when turnouts have been low.

Obama received 66% of the primary vote in Georgia when 22.7% of all registered voters in the state voted in the Democratic primary. In Virginia, Obama received 64% of the primary vote when 21.1% of all registered voters in the state voted in the Democratic primary. In Mississippi, Obama received 61% of the primary vote when 24.4% of all registered voters in the state voted in the Democratic primary.

Hillary Clinton received 67% of the primary vote in West Virginia when 30.1% of all registered voters in the state voted in the Democratic primary. In Pennsylvania, Clinton received 55% of the vote when 27.7% of all registered voters in the state voted in the Democratic primary. In Ohio, Clinton received 54% of the primary vote when 30.5% of all registered voters in the state voted in the primary.

There are exceptions (such as Arkansas, Tennessee, and Rhode Island), but Clinton, and not Obama, tends to win in the states where turnouts are higher. The relationship is strong enough that Democratic primary turnout can be predicted using Clinton’s share of the vote.