[Allan J. Lichtman is a professor of history at American University in Washington, D.C. His six books include Prejudice and the Old Politics: The Presidential Election of 1928 and The Keys to the White House. ]

The Democratic contest goes on, but as I predicted in my post two months ago, it is essentially over (“Is the Democratic Race Over?” February 19, 2008). To win the nomination, Hillary Clinton must win both North Carolina and Indiana on May 6. This is a nearly impossible task given the very favorable demographics for Barack Obama in North Carolina. Indiana remains a toss-up.

Contrary to the conventional wisdom, however, an ongoing nomination fight that may continue until the last contest in June, when the superdelegates will weigh in and settle the matter, should not hurt the Democrats in the fall campaign. Analysts have failed to distinguish between the party that holds the White House and the challenging party. A bitter, lasting battle hurts the incumbent party because it indicates problems with governing. Examples include Ronald Reagan’s challenge to President Gerald Ford in 1976, Ted Kennedy’s challenge to President Jimmy Carter in 1980, and Pat Buchanan’s challenge to President George H. W. Bush in 1992.

In contrast, struggles within the challenging party often indicate that the prize of the nomination is worth winning. The three greatest victories posted by challenging party candidates in American history all came after nomination struggles that lasted until the party convention. Warren Harding who won 60 percent of the popular vote in 1920 was nominated on the tenth ballot. Franklin Roosevelt who won 57 percent in 1932 was nominated on the fourth ballot and Dwight Eisenhower who won 55 percent in 1952 was nominated only after the convention seated his Texas delegation as opposed to a competing delegation pledged to his rival Robert Taft.

The fundamentals of election 2008 strongly favor a Democratic victory this fall as I explained in my post on the Keys to the White House (“The 13 Keys to the White House: Why the Democrats Will Win,” October 4th, 2007). However, presuming that Obama become the Democratic nominee it remains an unsettled question as to whether the nation is ready to elect an African-American president. According to exit polls, about a fifth of white voters in Pennsylvania’s Democratic primary said that race influenced their choice of candidates; these voters backed Clinton by 3 to 1 over Obama.

Unfortunately, it appears clear that some Republicans will launch a “Swift Boat” style campaign of vilification against Obama with a thinly coded racial animus. This campaign will not come directly from John McCain or Republican leaders. Rather, it will come from “independent groups” like Swift Boat Veterans for Truth or the National Security Political Action Committee that made Willie Horton the most familiar face of the 1988 campaign.

Already, the scurrilous attacks on Obama have begun. Floyd Brown, who created the Willie Horton ad, has put together a new ad that openly associates Obama with allegedly murderous gang members in Chicago. It features a roll call of gang victims and extensive footage of bleak and devastated ghetto neighborhoods in Chicago. It asks “can a man so weak in the war on gangs be trusted in the war on terror?”

It would be a tragedy if voters gave a very unpopular Republican Party another four years in the White House because of the skin color of the Democratic nominee. But I have enough faith in the American people to believe that this will not happen, no matter how many Willie Horton type ads the Republican surrogates chose to run in 2008.