Salena Zito

McMahon says the key to effective messaging is to summarize your point, then to offer the rationale. "The data that dial-testing provides helps candidates get there. It also helps insiders get inside a voter's head."

With the 2008 presidential election considered to be a wide-open affair, each party knows that swing voters are the key to winning. And the only way to win those voters is to get inside their heads to find out what phrase, word, delivery style or image will help capture their votes.

Voters, however, are funny. It's not always what you tell them that matters; it's what they hear.

Salena Zito

Salena Zito is a political analyst, reporter and columnist.