Campaign Puts New Strain on Secret Service

On the other hand, with more than 25 states proposing or holding caucuses or primaries by Feb. 5, the vast field could be cleared early, Price noted. Also, as a former first lady, Democratic candidate Sen. Hillary Rodham Clinton (N.Y.) already has a protective detail.

The reason for the Obama order is unclear. Sen. Richard J. Durbin (D-Ill.), who is backing Obama, expressed concern that the candidate is drawing large crowds that could impede his movement in an emergency, while Obama aides were concerned about threatening letters and Internet postings seeming to target the senator because of his race, congressional sources said, although there was no specific threat.

In interviews, Obama has expressed ambivalence about the change and played down any racial aspect.

"I'm not an entourage guy," Obama told ABC News, saying that until recently he helped his wife shop for groceries. But he added: "If I don't win it's not going to be because of my race. It's going to be because I didn't project a vision of leadership that gave people confidence."

While presidential candidates often object to Secret Service protection as intrusive and a barrier to voters, the agency's presence can convey legitimacy to fledgling campaigns and lend experience, organization and speed to their travel operations.

Former North Carolina senator John Edwards, who received a Secret Service detail in 2004 as the Democratic vice presidential candidate, has said he has no immediate plans to request protection this time. He told CNN that he would rather, "as long as possible, have the freedom to be able to be with people."

Spokesmen for the Republican front-runners, former New York mayor Rudolph W. Giuliani, Sen. John McCain (R-Ariz.) and former Massachusetts governor Mitt Romney, said the campaigns have neither asked for nor received Secret Service protection.

Staff writers Perry Bacon Jr. and Mary Beth Sheridan and political researcher Zachary A. Goldfarb contributed to this report.