National Review has the details:

“The mastermind behind the ballot-petition fraud was one Butch Morgan, then the Democratic-party chairman of St. Joseph County. With the help of three other employees of the county board of elections, Morgan faked names and signatures on ballot petitions that qualified Obama and Clinton for the May 6 Democratic primary. . . .

Clinton barely beat Obama in the Indiana primary, garnering 51 percent of the vote. The delegates were split almost evenly, with Clinton receiving 38 and Obama receiving 34. Had Obama been disqualified from the ballot and Clinton had received all 72 delegates, it would have put her within striking distance of the nomination. How would candidate Obama’s grassroots and financial support have been affected if he had been disqualified from the ballot and his campaign enveloped in a fraud scandal caused by local Democratic-party operatives?

Political momentum is a very delicate thing. It’s certainly possible that such a setback for Obama could have changed the outcome of the 2008 Democratic nomination contest. But of course, we will never know. All we do know for sure is that Indiana experienced election fraud committed by party activists that may have affected the 2008 election. But of course, according to some, there is no election fraud in the United States.”