For Democrats who gathered at their convention in the swing state of North Carolina, the high glitz extravaganza watched by millions on television was a partisan infomercial that has paid off, for the moment, in energizing their voters.

For Republicans who convened in the battleground state of Florida, the impact on the party faithful of their event has waned.

The Democratic convention in Charlotte last week revved up the base as a CNN/ORC International poll released Monday showed more Democrats than Republicans were enthusiastic about voting.

Although the difference between them is narrow at 59% to 57%, Republicans commanded a six-point edge, 62% to 56%, coming out of their convention.

"The Democratic convention was fairly well-received, particularly in comparison to the GOP meeting the previous week in Tampa," CNN Polling Director Keating Holland said about the latest figures.

Moreover, Democrats have gained substantially since a March survey when only 46% of respondents said they were enthusiastic about voting compared to 52% for Republicans.

The changes in voter enthusiasm within the parties also came as new polls showed shifting sentiment in the presidential race toward Democratic President Barack Obama.

The CNN poll showed Obama opening up a lead over his Republican challenger, Mitt Romney, after weeks of running even -- 52% of likely voters nationwide backed Obama, compared to 46% for Romney. A Gallup survey released on Sunday also showed Obama with a wider lead.

But a Washington Post-ABC News poll of likely voters also released Monday showed the race still neck-and-neck with Obama at 49% and Romney at 48%.

Stronger messaging

Until the presidential debates beginning on October 3, any new momentum depends on the ability of both campaigns to drive home their message, political experts say.

Democrats say: Give Obama another four years to move the country forward.

Republicans say: Fire the president and replace him with Romney, a proven business leader.

The work of taking those messages to a broader national audience began at the carfefully crafted conventions.

Republicans showed sepia toned images of unemployed workers as speakers roundly criticized what the party sees as Obama's failures on the economy.

The Democrats projected brightly colored photos of happy entrepreneurs on stage and warned that this Technicolor vision could fade if the nation returned to the policies of previous Republican administrations.

Both sought to suggest an answer to the question: "Are you better off now than you were four years ago?"

"There are many layers of the performance going on," said Daniel Kreiss, an assistant professor of political communications at the University of North Carolina, noting images, speeches and biographies.

"The political performance and political theater is a good thing for democracy. It's one of the few ways the parties get a chance to make their unmitigated case for that hour," Kreiss said.

Both conventions featured movie-quality videos of voters talking about either their economic woes or triumphs. Staffers moved quickly among crowds to ensure the signs held by delegates had exactly the right messages when flashed across television screens back home.

Powerful images

Both conventions played up patriotism with plenty of flag waving and the parties promoted American-themed images, said Kreiss, who wrote the book, "Taking Our Country Back: The Crafting of Networked Politics from Howard Dean to Barack Obama."

At the Republican convention, many of the supplied signs read "We Built It" in red, white, and blue writing. At the Democratic event, similar signs read "Economy Built to Last."

One thing that stood out in Tampa was Romney's biopic, which Kreiss said "had powerful images of the candidate" turning things around.

Images at the Democratic convention included people who would be small business owners and signs indicating they were open for business.