On February 10, 2007, Barack Obama, then-junior United States senator from Illinois, announced his candidacy for the presidency of the United States in Springfield, Illinois. Obama announced his candidacy at the Old State Capitol building, where Abraham Lincoln had delivered his "House Divided" speech. Obama was the main challenger, along with John Edwards, to front-runner Hillary Clinton for much of 2007. He had only recently emerged as a national figure in Democratic politics, having delivered the DNC keynote address just three years prior and won his Senate election shortly thereafter.

Obama's initial victory in the Iowa caucus in January 2008 helped bring him to national prominence from a crowded field of Democratic challengers. Obama benefited from early support from prominent Democrats including Tom Daschle and Ted Kennedy, and his campaign began to trade a series of hard-fought state wins with Clinton through Super Tuesday, in which Obama had great success in large rural states and Clinton was nearly as dominant in high-population coastal areas. Obama continued to have success in small donor fundraising, and continued winning a greater number of contests than Clinton through April.

In early May, after Obama won the North Carolina primary and narrowly lost the Indiana primary, superdelegates began to endorse Obama in greater numbers. Obama's win in Oregon gave him an absolute majority of the pledged delegates. After a rush of support for Obama from superdelegates on June 3, the day of the final primary contests of Montana and South Dakota, Obama was estimated to surpass the 2,118 delegates required for the Democratic nomination. On June 7, Clinton formally ended her candidacy and endorsed Obama, making him the party's presumptive nominee.

On August 27, 2008, at the Democratic National Convention, the Democratic Party formally nominated Barack Obama to run for the office of the President of the United States of America. Obama would go on to win the presidential election against Republican nominee John McCain.