In fact, debates have become more influential as their number increases and clips show up on YouTube, he said. Some of their punch comes from news media conclusions that a certain candidate performed strongly or weakly, judgments that can sway voters without a strong preference, said John Geer of Vanderbilt University.
Similarly, a poorly known candidate can pick up support by winning primaries, because that attracts news coverage, usually positive, Geer said.
The news coverage played a role for Mark Fratella, a 34-year-old algebra teacher in Chicago. At various times he favored Romney and Gingrich, but finally settled on Santorum for the upcoming Illinois primary.
"My wavering at the beginning seemed to go with whoever was the front-runner at the time, just because of the coverage," Fratella said. The media attention finally prodded him to focus on Santorum, and what he found "resonates with me."
Candidates are also helped by endorsements from iconic organizations that voters trust — a "huge" help in a race that lacks party labels, Lupia said.
So as all this information flows in, how does a voter weigh it and come to a decision? It's a mix of the conscious and unconscious, gut feeling and rational consideration.
Experts debate whether voters consciously know why they voted for one candidate over another, Redlawsk said. One school of thought suggests voters combine information about each candidate in sort of a mental ledger to produce an overall impression, he said, but once that's done, they forget the specific information that influenced them.
"We take into account a lot more information than we can report back later when we're asked," he said.
In any case, many experts say that for all the challenges, primary voters do a fairly good job of choosing.
Although Lau's study suggests their votes don't always go to the "right" candidate, even a "wrong" candidate is probably not very different, Redlawsk says.
Popkin calls the primary system "amazing," a process that weeds out "Johnny-one-notes" and lightweights.
"I think it works better than people realize."
Malcolm Ritter can be followed at http://www.twitter.com/malcolmritter
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