C.J.'s first day as Chief of Staff gives her a new appreciation for Leo's skill in the role. While struggling to keep up with her hectic schedule, she must handle the sudden appearance of abandoned Soviet nuclear material, counter political maneuvering within the Cabinet, and assert her authority with the staff and the President. Toby conducts a press briefing after which C.J. orders him to quickly find someone to fill the role permanently. The Democratic Party enlists Josh's help to talk Congressman Matt Santos out of taking an early retirement.

Josh and Santos visit New Hampshire to launch the presidential campaign. Josh has experience running national campaigns and has a clear idea about what candidates should and shouldn't do to get elected, but Santos's approach differs dramatically: he believes in talking about big ideas rather than saying whatever he needs to do in order to win votes. This difference in opinion combined with conventional wisdom that says Santos has no chance of winning threaten to sink the campaign before it's begun. Will and Donna are also in New Hampshire, running Vice President Bob Russell's campaign - which puts their interests at odds with those of the Santos campaign.

A day in the lives of presidential candidates Bob Russell, Matt Santos, and Arnold Vinick, who are in Iowa trying to gain support for their campaigns. Iowa is the first state in the nation to hold their presidential caucuses, and issues affecting farmers and rural areas are the focus. The most important issue on the table is the large federal subsidies for ethanol fuel given to corn growers, which is supported by Iowa residents but seen as naked pandering by the rest of the country. Josh continues to clash with Santos over winning votes instead of proposing radical policy. Donna and Josh continue to avoid speaking about the state of their relationship.

Five days before the New Hampshire Democratic primary, the Santos campaign risks extinction as Matt has not been invited to the last debate. Josh proposes a number of strategies to get Santos into the debate, including deal-making, legal challenges, attack ads, and publicity stunts - but the Congressman is reluctant to play along. With Josh scrambling to keep the campaign alive, Santos calls in help from Washington to tune his message. Hoynes and Russell launch attack ads on each other's records, and Josh realizes that a desperate long-shot is needed to keep Santos in the race.

Back in Washington briefly, Josh visits the White House and is surprised to discover that as a campaign manager he is no longer part of the inner circle in an administration that wants to remain neutral in the Democratic primary. Toby is the focus of some concern after being more withdrawn than usual and also because he is nursing a cut on his face that he doesn't want to talk about. Charlie tells Kate that a guy at his gym has been asking about her, but she's unsure if she's ready to date again. A multi-state water rights fight pitches C.J. against lobbyist Cliff Calley, who proves to be both infuriating and intriguing. Josh and Donna are both suspicious when far-left Senator Rafferty joins the race, obviously as a spoiler candidate.

Hoynes and Russell are campaigning in New York, confident of their prospects in the California primary. Santos needs to do unexpectedly well in California in order to stay financially afloat; another third place finish will see his donors shift their money elsewhere, finishing his campaign. Santos's message of education and health care is overshadowed when California passes a law prohibiting drivers licenses for illegal immigrants. Despite the bill being widely supported by most voters, Matt cannot publicly endorse it as he's counting on the support of Latino voters, who expect him to denounce it.

While Vinick and the Republicans deliver a flawless albeit predictable convention, the Democratic convention looks to be more like a pie fight as there is no clear favorite. Russell tries to preempt the floor vote by hinting offers of the vice presidential nomination to both Santos and Governor Baker of Pennsylvania. Charlie and Zoey's relationship is becoming more serious, resulting in different reactions from the President and the First Lady. An air leak on the International Space Station will kill all three astronauts unless a rescue mission can be launched. NASA advises that their shuttles are unfit for flight, but then hints at another solution.

WHO WILL BE THE DEMOCRATIC PRESIDENTIAL CANDIDATE? - It's the Democratic National Convention and the race to become the Democratic Presidential candidate has narrowed to three candidates: Russell, Baker and Santos. Also, Bartlet must wrestle with the decision to launch the super-secret defense shuttle to rescue the astronauts trapped at the space station and risk national security or let them die.

Four days after the Democratic convention, Josh begins to staff up the Santos campaign. With Santos and Leo effectively strangers - and Leo not an experienced campaigner - adjustments of roles and responsibilities are required in order to deliver a strong and consistent message. The White House prepares to launch the military Space Shuttle on its rescue mission to the Space Station amidst growing suspicion that proof of its existence was deliberately leaked by someone in the Administration. The Republicans offer Bartlet a concession on an education bill in an attempt to drive a wedge between him and the Santos campaign.

Despite vigorous campaigning, the Santos campaign still struggles to articulate its message and keep the focus on domestic issues rather than gossip and trivia. Although Santos served decades in the military and remains in the reserves, Vinick still appears the stronger candidate on national security issues due to stereotypes about Republicans and Democrats. The White House's decision to halt their own investigation into the leak is a savvy legal move, however it could prove to be costly politically: while Vinick can slam the President for this decision, it's not so easy for Santos to do so. Josh reluctantly recruits help with running the campaign when it becomes obvious that he's trying to do too much himself.

The Santos campaign faces questions on intelligent design and evolution during a campaign stop focusing on education in Pennsylvania. Margaret testifies before the committee investigating the leak, which has also served most current and former members of the Bartlet administration with subpoenas. A suicide bombing in the Middle East throws the region into chaos and threatens to postpone all campaigning. An intelligence analyst assigned to brief the Vinick campaign demands to speak with CJ.

Toby's confession sends shock waves through the White House; Kate tracks developments following the assassination in Kazakhstan; the Santos campaign appears stalled.

The Santos campaign's difficulties with the black community continue when a Latino police officer shoots a black child; C.J. offloads preparations for Ellie's wedding to Will when Kate needs her help with Kazakhstan; Josh visits Toby.

Leo's preparation for the Vice Presidential debate is going badly; Santos makes his last trip home before the election; Will and Kate continue to flirt.

The Vinick campaign struggles with the impact of the nuclear accident in California; Josh and Donna have a "moment".

Election day finally arrives; C.J. ponders job offers; the election looks too close to call.

Polls are closing across the country, and the race is too close to call; friends and colleagues react to the news about Leo.

President Bartlet and his current and former staffers come together for Leo's funeral.

Eyebrows are raised when the President-elect places a call to the president of China and offers a different position than that of Bartlet. Meanwhile, Josh picks his deputy chief of staff.

While Santos is wrapped up in choosing his new Vice President, Helen is overwhelmed by the issues facing the new First Family. Meanwhile, Vinick must find a new road now that the election is over.

Two weeks before the inauguration, CJ and the rest of the Bartlett administration consider what they will do next. CJ examines her relationship with Danny and considers whether or not to suggest to the President pardoning Toby.

Santos and his staff prepare for the inauguration as Bartlet and his team look back on their years in the White House.