The primary election was held on May 9, 2006. Pete Ricketts won the Republican nomination with 48% of the vote. Ben Nelson was unopposed for the Democratic nomination. Nelson was elected in 2000 by a margin of 51% to 49% after serving as the state's governor for two terms. Nelson, considered the most conservative Democrat in the Senate, is the lone Democrat in Nebraska's Congressional delegation. This election was one of the most expensive in Nebraska history. In 2005, Ben Nelson raised $3.9 million for his re-election campaign. Pete Ricketts contributed $14.35 million of his own money to his campaign; he raised an additional $485,000 in contributions. The race also attracted national attention and generated several high-level campaign appearances. President George W. Bush appeared at a rally for Ricketts on November 5, 2006, in Grand Island, while then-U.S. Senator Barack Obama appeared at a fundraiser for Nelson and other Nebraska Democrats on May 5, 2006 in Omaha. However, he won re-election by a wide margin.