CHARLOTTE, N.C. -- San Antonio Mayor Julian Castro energized the Democratic National Convention on Tuesday night with 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 excite the party's base and electrify Latino voters of all political persuasions who could be decisive in the November election.Latinos took center stage on opening night of the Democratic National Convention. Not only was Castro the first Latino to give the keynote address, but in a speech that hammered the theme of opportunity and honored the hard work of older generations so that the young could prosper, he spoke to the highest number of Latino delegates, 800, at any presidential convention."America didn't become the land of opportunity by accident," Castro said. Many in the crowd waved orange campaign signs that read, "Oportunidad."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 Latino populations. And Latino delegates in North Carolina are reminding supporters that President Barack Obama won the Tar Heel State by a mere 14,000 votes. Exit polls showed Obama received 26,000 more Latino votes than Sen. 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.Castro stuck to Obama's campaign script focusing on the middle class. Recalling the work of his grandmother and his mother, who was sitting in the audience, he said of them: "They believed opportunity created today would lend to prosperity tomorrow."Castro criticized GOP candidate Mitt 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. "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.Democrats need Castro's help erasing a four-point bump that 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, Fla. Romney's support is now 30 percent among Latinos polled, up from 26 percent the week before, according to a new poll.