The Potomac primary (named after the river that splits the region), also called Chesapeake Tuesday, the Beltway primary, and the Crabcake primary, is the confluence of three Democratic presidential primaries and three Republican presidential primaries that takes place after Super Tuesday.

The results on both sides were fairly unsurprising according to opinion polling, with both John McCain and Barack Obama winning by substantial margins. For Obama, however, the race had been significant as a major source of delegates in the close Democratic race, with him garnering a net gain of 50 delegates.

President Barack Obama is running unopposed.

Barack Hussein Obama II (ⁱ/bəˈrɑːk huːˈseɪn oʊˈbɑːmə/; born August 4, 1961) is the 44th and current President of the United States. He is the first African American to hold the office. In January 2005, Obama was sworn in as a U.S. Senator in the state of Illinois. He would hold this office until November 2008, when he resigned following his victory in the 2008 presidential election.

Born in Honolulu, Hawaii, Obama is a graduate of Columbia University and Harvard Law School, where he was the president of the Harvard Law Review. He was a community organizer in Chicago before earning his law degree. He worked as a civil rights attorney in Chicago and taught constitutional law at the University of Chicago Law School from 1992 to 2004. He served three terms representing the 13th District in the Illinois Senate from 1997 to 2004.

Following an unsuccessful bid against the Democratic incumbent for a seat in the United States House of Representatives in 2000, Obama ran for the United States Senate in 2004. Several events brought him to national attention during the campaign, including his victory in the March 2004 Illinois Democratic primary for the Senate election and his keynote address at the Democratic National Convention in July 2004. He won election to the U.S. Senate in Illinois in November 2004. His presidential campaign began in February 2007, and after a close campaign in the 2008 Democratic Party presidential primaries against Hillary Rodham Clinton, he won his party's nomination. In the 2008 presidential election, he defeated Republican nominee John McCain, and was inaugurated as president on January 20, 2009. Nine months later, Obama was named the 2009 Nobel Peace Prize laureate. In April 2011, he announced that he would be running for re-election in 2012.

John Sidney McCain III (born August 29, 1936) is the senior United States Senator from Arizona. He was the Republican presidential nominee in the 2008 United States election.

McCain followed his father and grandfather, both four-star admirals, into the United States Navy, graduating from the U.S. Naval Academy in 1958. He became a naval aviator, flying ground-attack aircraft from aircraft carriers. During the Vietnam War, he was almost killed in the 1967 USS Forrestal fire. In October 1967, while on a bombing mission over Hanoi, he was shot down, seriously injured, and captured by the North Vietnamese. He was a prisoner of war until 1973. McCain experienced episodes of torture, and refused an out-of-sequence early repatriation offer. His war wounds left him with lifelong physical limitations.

He retired from the Navy as a captain in 1981 and moved to Arizona, where he entered politics. Elected to the U.S. House of Representatives in 1982, he served two terms, and was then elected to the U.S. Senate in 1986, winning re-election easily four times, most recently in 2010. While generally adhering to conservative principles, McCain at times has had a media reputation as a "maverick" for his willingness to disagree with his party on certain issues. After being investigated and largely exonerated in a political influence scandal of the 1980s as a member of the Keating Five, he made campaign finance reform one of his signature concerns, which eventually led to the passage of the McCain-Feingold Act in 2002. He is also known for his work towards restoring diplomatic relations with Vietnam in the 1990s, and for his belief that the war in Iraq should be fought to a successful conclusion. McCain has chaired the Senate Commerce Committee, opposed spending that he considered to be pork barrel, and played a key role in alleviating a crisis over judicial nominations.