CHARLOTTE, N.C. -- San Antonio Mayor Julian Castro was expected to walk onto the stage Tuesday night and share the story of how his grandmother came from Mexico to build a life in the United States, ultimately leading to his time in the spotlight - and Democrats were counting on him to energize the party's base and electrify Latino voters of all political persuasions who could be decisive in the November election.

Latinos were to take center stage on opening night of the Democratic National Convention. Not only was Castro the first Latino to give the keynote address, but he would be speaking to the highest number of Latino delegates, 800, at any presidential convention.

Latino voters are being wooed by both Democrats and Republicans to a degree never seen before.

The fastest-growing voter bloc could be the difference in November, as the election will likely be decided in battleground states such as Florida and Colorado that have large Hispanic populations. And Latino delegates in North Carolina are reminding supporters that Obama won the Tar Heel state by a mere 14,000 votes. Exit polls showed Obama received 26,000 more Latino votes than John McCain, according to the Immigration Policy Institute.

At a Hispanic Caucus meeting, delegate Matty Lazo-Chadderton called on South Carolina Latino delegates to come to Charlotte to help mobilize Latinos in the state.

"We're fired up," said Lazo-Chadderton, a Cary, N.C., delegate originally from Peru. "We're walking the walk. The Hispanic vote is more important than people realize."

Latinos make up just a fraction of North Carolina's 6.4 million registered voters, but their voter registration numbers have doubled in the past four years. Arturo Vargas, executive director of the National Association of Latino Elected and Appointed Officials, said Latinos could decide the state if they vote in a bloc.

"Everyone wants to be asked to the dance," he said. "The key here is that there will be no majority party in this country without participation from Latinos. We're already 16 percent of the population, 9 percent of the voters. It's only going to increase."

Castro was expected to stick to President Barack Obama's campaign script focusing on the middle class. In excerpts of his speech released by the campaign earlier Tuesday, Castro criticized Romney for failing to understand the challenges most Americans face and that sometimes they can use a little help.

"Republicans tell us that if the most prosperous among us do even better, that somehow the rest of us will too," he said, according to the prepared speech. "Folks ... we've heard that before."

Rep. Debbie Wasserman Schultz, chairwoman of the Democratic National Committee, warned Latinos at a Hispanic Caucus meeting this week that a loss for Obama would be devastating for Latinos who have benefited from Obama's policies, including a new health care law and deferred deportations for young undocumented immigrants. Approximately 32 percent of Latinos were uninsured in 2009, higher than any other racial or ethnic group, and half of Latinos did not have a regular doctor, compared with only one-fifth of white Americans, according to the White House.

She declared this race "personal ... for so many Americans, but particularly for Hispanic Americans."

"Julian Castro is one of the key rising stars in our party," Wasserman Schultz said.

Democrats need Castro's help erasing a four-point bump that GOP candidate Mitt Romney received after bringing out a list of prominent Latino Republican elected officials, including superstar U.S. Sen. Marco Rubio of Florida, at the Republican National Convention last week in Tampa. Romney's support is now 30 percent among Latinos polled, up from 26 percent the week before, according to a new impreMedia/Latino Decisions poll released Monday.

Obama continues to enjoy more than 60 percent support from Latinos, but Vargas said it's a misconception to believe that Latinos will automatically line up behind any candidate.

Many experts like to point out that McCain received only 31 percent of the Latino vote in 2008, according to some exit polls, as an example of Republicans diminishing sway among Latinos. But Vargas notes that George W. Bush garnered 44 percent of the Hispanic vote in 2004.

The Republicans' stance against illegal immigration has turned many Latinos off of the Republican Party. Romney has advocated for "self-deportation" and criticized Obama for granting hundreds of thousands of young undocumented immigrants a reprieve from deportation.

But leading Republicans have been pushing from inside the party for a more moderate tone on immigration. Rubio introduced a proposal similar to Obama's for young undocumented immigrants this year. And former Florida Gov. Jeb Bush opened his speech at the GOP conventions in Spanish: "Bienvenidos a Florida!" And in a speech sponsored by the Hispanic Leadership Network, Bush advocated against the hard-line approach and said the Republican Party could to appeal to Latinos "if we just stop acting stupid."

Latinos' historically strong Catholic and Christian faith fit well with Republican ideals. Many oppose Democratic issues such as support for same-sex marriage and abortion rights.

Latinos are the "ultimate swing voters," said Janet Murguia, president of the National Council of La Raza. And many Latinos are recently naturalized citizens without "a life-long affinity to a particular party," said Monica Lozano, chief executive officer of impreMedia, a Hispanic news company.

Voter turnout among Latinos is key for both parties as they enter the critical last two months of the campaign, Lozano said. Latinos for Obama and Juntos con Romney have very well-developed strategies, she said.

They're using televisions and radio advertising, social media and online town halls aimed at influencing this constituency.

"Every tool has now been fully deployed," Lozano said. "This is without a doubt the most sophisticated and comprehensive effort to reach Hispanic voters in our political history."