The people who vote in presidential primaries might be more partisan than the median voter, but that says nothing about their overall knowledge of the political process, or the candidates in particular. For the most part, presidential primaries are low-information elections: Few voters know anything about the candidates outside of what they learn from media, and the circumstances of presidential primaries—a relatively short window for campaigning, multiple candidates, and the fact that everyone belongs to the same party—make it difficult for voters to form strong opinions. Go to almost any primary event in any state, and you’ll meet a large number of attendees who are there with an open mind—they just want to see what the candidate "is all about.”
Under these circumstances, money goes a long way. Regardless of the content, sustained advertising can shape the electorate and bring low-information voters to one side or another. Look no further than the major Super Tuesday races for evidence of this. In Tennessee, Rick Santorum finished February with 40 percent support—a massive 21-point lead over Mitt Romney, who earned 19 percent support from the state’s voters. But in the week that followed, the pro-Romney Restore Our Future super PAC pumped more than $1.4 million worth of anti-Santorum ads into the state, swamping the efforts of the former Pennsylvania senator by a factor of 10. By the beginning of this week, according to Public Policy Polling, only 34 percent of voters backed Santorum's bid for the nomination, while Romney could claim a 10-point gain.
The same was true for Ohio, where last week’s polling gave Santorum 37 percent support to Romney’s 26 percent support. After one week and $2.8 million in anti-Santorum advertisements, however, Santorum lost his lead and Romney turned the election into a toss-up. The former Pennsylvania senator wasn’t helpless—he spent more than $1 million—but he was overwhelmed. In the most recent poll from Quinnipiac University, Romney earns 34 percent support to Santorum’s 31 percent.
The important thing about all of this is what it doesn’t say. Money was a necessary part of Mitt Romney’s quest to catch up with Santorum in those two states, but it wasn’t sufficient to the task; if Santorum had had six months or a year to build his reputation—and thus seed more information—the change wouldn’t have been so dramatic. But as long as we’re dealing with low-information voters, we should expect to see the potency of money.