Mark Potok, a civil rights expert at the Southern Poverty Law Center, has been tracking the views of white supremacists for years.
Last February, he noticed an increase in racist attacks and threatening remarks about Obama on the Internet.
"There is plenty of unpleasant stuff out there, "N***** this, N***** that" and it's been going on for the better part of six months," he said.
But since then, the level of vitriol has remained stable. "I don't think there's been any big increase in the kinds of things we're seeing," Potok says, adding that many of the white supremacist sites know that they're being monitored and users tend to be careful about posting violent threats.
Potok passes along violent threats to the Department of Homeland Security, including a recent e-mail sent to the Southern Poverty Law Center that warned: "ATTENTION, IF OBAMA BECOMES PRESEDANT I WILL KILL HIM MYSELF MAKE NO MISTAKE ABOUT IT."
Prominent white supremacists, including former Louisiana state representative and Ku Klux Klan Grand Wizard David Duke, have condemned Obama in subtler terms.
Duke recently issued a statement denouncing Obama for his ties to the Rev. Jeremiah Wright, the candidate's former pastor who stirred up controversy with his conspiracy theories, and because his "ultimate loyalty" lies with "his fellow African-Americans."
While previous African-American presidential candidates, such as the Rev. Jesse Jackson, were the target of racist threats, they were not campaigning in the age of the Internet and they were not nearly as successful as Obama.
The real possibility that an African-American could win the White House in November, along with the anonymity of the Web, which lends itself to expressing extreme views, has galvanized a certain segment of the population, explains John G. Geer, political science professor at Vanderbilt University.
"Is Obama being black raising security issues, the answer is, unfortunately, yes," he says. "Because there are more people out there, hate groups who are going to make certain kinds of statements and claims that will alert the Secret Service to be on their guard."
"There is a portion of the population who will be very unhappy about Obama, not due to his policies but simply because he's black, and there will be even more of an increase in these racist views as the general election rolls around."
In addition to the hate spouted by extremists, race has become an issue for the candidate in other, more subtle ways.
In exit polls taken after the recent West Virginia primary, two in 10 white voters said the race of the candidate was a factor in their vote, second only to the numbers in the exit poll in Mississippi. Sixteen percent of white voters in Pennsylvania, West Virginia, North Carolina, Indiana, Kentucky and Oregon say that race was an important factor in their vote, according to an ABC News analysis of exit polls from those states.
Obama recognized that race had been an issue in the campaign, particularly after the South Carolina primary, during his speech on race in March. He acknowledged the country's racial stalemate but asserted that "Contrary to the claims of some of my critics, black and white, I have never been so naive as to believe that we can get beyond our racial divisions in a single election cycle, or with a single candidacy — particularly a candidacy as imperfect as my own."