Jeff Bliss Tue Mar 11, 12:04 AM ET March 11 (Bloomberg) -- The political passions stirred by the Democratic presidential battle between the possible first black nominee and the possible first woman are also stirring security concerns on the part of the U.S. Secret Service. ADVERTISEMENT The agency began providing protection to candidates earlier this year than in any previous election in response to crowds that have sometimes topped 30,000, a record for the primary season, spokesman Darrin Blackford said. The excitement of the race pitting Illinois Senator Barack Obama against New York Senator Hillary Clinton ``definitely adds something the Secret Service hasn't seen in a while,'' said Andrew O'Connell, a special agent in the 1990s who is now a managing director at New York-based Fortress Global Investigations and Security Corp. Besides the fact that Obama is the first black candidate with a chance to win the party nomination, Clinton is a ``polarizing figure'' dating back to her time as first lady, O'Connell said. Obama, 46, began receiving protection in May 2007, 18 months before the November 2008 election. That was the earliest for any candidate since the practice was instituted following the 1968 assassination of Senator Robert F. Kennedy, shot by Sirhan Sirhan at the Ambassador Hotel in Los Angeles moments after claiming victory in the California primary. Clinton and McCain Clinton, 60, has had protection since 1992, when her husband, former President Bill Clinton, became the Democratic nominee. Arizona Senator John McCain, 71, hasn't had Secret Service coverage, though he will get it now that he has won enough delegates to clinch the Republican nomination. The Secret Service began covering the 2004 Democratic nominee, Senator John Kerry of Massachusetts, seven months before the election. President George W. Bush, then the governor of Texas, received his detail eight months before the November 2000 vote. Obama -- whose Secret Service codename is ``Renegade'' -- got his protection at the prompting of Richard Durbin, a fellow Illinois senator and supporter. Durbin, the No. 2 Senate Democrat, saw thousands of people showing up for early campaign rallies when only hundreds had been expected, said Joe Shoemaker, his spokesman. ``Roads would be choked with cars,'' blocking escape routes in the event of an incident, Shoemaker said. `Special Concern' House Homeland Security Committee Chairman Bennie Thompson, like Durbin an Obama supporter, wrote Homeland Security Secretary Michael Chertoff on Jan. 9 that ``the national and international profile of Senator Barack Obama gives rise to unique challenges that merit special concern.'' Thompson's panel oversees the Secret Service, which is part of Chertoff's department. Another black presidential candidate, the Reverend Jesse Jackson, received Secret Service protection for his 1984 and 1988 runs a year before Election Day. Obama's wife, Michelle -- codenamed ``Renaissance'' -- received protection at the request of the campaign on Jan 29. Jen Psaki, a campaign spokesman, declined to comment on the reasons. While Obama has inspired comparisons with John F. Kennedy and Martin Luther King Jr. among his supporters, some of them are taking the comparison too far, said former Dallas Mayor Ron Kirk, an Obama backer. Kirk said he has read Internet postings from blacks saying ``we shouldn't even nominate him, because if we do something bad will happen.'' `Stop Worrying' Obama has ``the best security in the world, and people should stop worrying,'' said Robert Gibbs, the candidate's spokesman. As Obama gave a speech in San Antonio on the night of the March 4 primaries, four sharpshooters were positioned on two towers behind him while four plainclothes agents stood near him. Three helicopters circled above, a level of security that is common for Obama and Clinton at large events. At least seven agents surrounded Obama at a March 4 rodeo in Houston. At rallies, agents in T-shirts printed with Obama's likeness melt into the crowd. While a news report that the Secret Service had stopped scanning participants at a Feb. 20 rally in Dallas's Reunion Arena sparked criticism on the Internet, Blackford, the Secret Service spokesman, said the agency never intended to put everyone through magnetometers. ``We don't rely on any one measure,'' he said. ``The plans are multilayered.'' White Supremacists In the past month, animosity toward Obama has increased on white supremacist Web sites, said Mark Potok, director of the intelligence project at the Southern Poverty Law Center in Montgomery, Alabama. He said that while he didn't know of any specific threats, ``the tone has begun to heat up.'' Security for Clinton -- codename ``Evergreen'' -- was tightened in January, when the Secret Service began requiring people at rallies to walk through scanners. On the candidate's plane, rows of agents separate her from the press corps. The toughest events to secure are those that are scheduled and public, O'Connell said. In assessing threats, the Secret Service monitors groups and people who have been a problem in the past, rating the risk they present, he said. Those deemed most dangerous are put under surveillance. Agents are trained to handle a politician's interaction with the public, including handshakes and posing for pictures, he said. Joe Russo, who was in charge of the Clintons' Secret Service detail until 2004, said presidential campaigns often create a conflict between the need for exposure and security. The candidates ``have to be out there,'' he said. ``You can't restrict them.'' To contact the reporter on this story: Jeff Bliss in Washington at email@example.com .