CHARLOTTE, N.C. — Some time around 10:00 p.m. Tuesday's Democratic National Convention transformed itself abruptly: The volume came down, the soft focus came on, and the party switched its focus from one audience to the next.

The switch into prime time marked a Democratic effort to run two parallel conventions: One hard-edged pitch to the party's base; and one broad, warm appeal to swing voters. The beginnings of Tuesday's convention were marked by fiery, shouted denunciations of Mitt Romney's wealth and and by relentless warnings about Republican views on women's health and quips like former Ohio Gov. Ted Strickland's: “If Mitt was Santa Claus, he’d fire the reindeer and outsource the elves." The program swerved when prime time hit and broadcast viewers arrived, however, quickly becoming conciliatory and emotionally warm, closed by Michelle Obama's personal speech.

And that split in messaging — structured around the different audiences of cable and broadcast television — reflects the Obama campaign's basic challenge: They must re-animate a party base whose interest and engagement have faded since 2008, and who they believe are watching the convention closely, whether inside the Time Warner Arena or on MSNBC or another cable news outlet; and they must answer a week-long Republican effort to court the less-engaged swing voters in Ohio and Virginia who will ultimately decide the election, and who will come across the convention, at best, for its hour of prime time.

In the first track of the convention, an unapologetic, full-throated Democratic assault on from figures like Strickland and Senate Majority Leader Harry Reid showed little restraint toward Mitt Romney, who was criticized for withholding his tax returns, for his Swiss bank account, and for his trouble connecting with average Americans. It was designed to be replayed countless times on cable TV and YouTube — the home of the political junkies who devote time and money to the Obama effort. Inside the Time Warner Arena, each attack drew the crowd of party faithful to their feet, cheering or booing as the moment demanded.

"Mitt Romney says we should take his word that he paid his fair share," Reid shouted. "His word? His word? Trust comes from transparency, and Mitt Romney comes up short on both."

And it included a broad defense of some of Obama's most liberal, and least popular, policies. The beginning of the night dwelled not just on attacking Romney but on President Obama's signature progressive policy move, the 2010 health care overhaul. "I am shocked how much we are talking about ObamaCare," a Democratic operative noted.

That first convention seemed to contradict the promise last week of Obama deputy campaign manager Stephanie Cutter.

"The goal of our convention is to bring the choice in this election into sharp focus,”she said last last week. “It won't be about rallying the base or leveling petty attacks.” But the easiest way to sum up the first day of the Democratic convention might be a combination of both those things.

But the blend of liberal policy and hard-edged attacks played well in the room.

"It just showed stark differences," said Cindy Trigg, a Nevada delegate. "It showed one party leadership over the other party leadership, period."

Any surprise at the intensity of Democratic appeals to the party base Tuesday, however, turned abruptly into the realization at 10:00 p.m. that the party had begun a second act. There Julian Castro, the young San Antonio mayor, spoke in broad terms about opportunity and a contrast of visions. Then second, First Lady Michelle Obama offered a heartfelt depiction of her husband’s private side.

The second convention more closely mirrored the Republican effort in Charlotte last week. There, a central goal seemed simply to rebrand the party as young, diverse, and ultimately moderate, a vision embodied by figures like former Secretary of State Condoleezza Rice and New Mexico Gov. Susana Martinez. Republicans will rely on Obama to rally their base, and they eschewed the shouted attacks that dominated the opening of the Democratic Convention.

Democrats, by contrast, have chosen not to choose. Battling over disillusioned Obama 2008 voters, the Republican message in Tampa was simple: In Charlotte the dual message is that Republicans are unacceptable to moderates, and that the dream of 2008 should still be alive for partisan Democrats.

Whether Democrats can pull off their messaging split, and keep the edgy early evening from spilling over into prime time, is as much a bet about how Americans consume news as about the substance of the message. And the Republican Party spent the evening trying to make Strickland, not Obama or Castro, the face of the convention. "The Democrats," complained GOP spokesman Tim Miller, "launched their convention with petty, partisan attacks."