2004 U.S. Senate campaign

In mid-2002, Obama began considering a run for the U.S. Senate; he enlisted political strategist David Axelrod that fall and formally announced his candidacy in January 2003.Decisions by Republican incumbent Peter Fitzgerald and his Democratic predecessor Carol Moseley Braun not to contest the race launched wide-open Democratic and Republican primary contests involving fifteen candidates. Obama's candidacy was boosted by Axelrod's advertising campaign featuring images of the late Chicago Mayor Harold Washington and an endorsement by the daughter of the late Paul Simon, former U.S. Senator for Illinois.He received over 52% of the vote in the March 2004 primary, emerging 29% ahead of his nearest Democratic rival.

In July 2004, Obama wrote and delivered the keynote address at the 2004 Democratic National Convention in Boston, Massachusetts.After describing his maternal grandfather's experiences as a World War II veteran and a beneficiary of the New Deal's FHA and G.I. Bill programs, Obama spoke about changing the U.S. government's economic and social priorities. He questioned the Bush administration's management of the Iraq War and highlighted America's obligations to its soldiers. Drawing examples from U.S. history, he criticized heavily partisan views of the electorate and asked Americans to find unity in diversity, saying, "There is not a liberal America and a conservative America; there's the United States of America." Though it was not televised by the three major broadcast news networks, a combined 9.1 million viewers watching on PBS, CNN, MSNBC, Fox News and C-SPAN saw Obama's speech, which was a highlight of the convention and confirmed his status as the Democratic Party's brightest new star.

Obama's expected opponent in the general election, Republican primary winner Jack Ryan, withdrew from the race in June 2004. Two months later and less than three months before Election Day, Alan Keyes accepted the Illinois Republican Party's nomination to replace Ryan. A long-time resident of Maryland, Keyes established legal residency in Illinois with the nomination. In the November 2004 general election, Obama received 70% of the vote to Keyes's 27%, the largest victory margin for a statewide race in Illinois history.