Some candidates run for president with the real expectation and goal of winning, others have other motivations. A third category exists of those who had a real expectation of winning but then realize they cannot win, and convert their campaign into a cause.
In 2004, US Rep. Dennis Kucinich (D-OH) ran thinking he would be the anti-war candidate. Too bad for him, Gov. Howard Dean (D-VT) decided to switch his campaign's emphasis from health care and balanced budgets to the Iraq war and the problems of the Democratic Party. Both lost badly, although there was a moment there where all the other candidates realistically though Dean would be the nominee. However, neither man's effort was in vain. The war went from popular from unpopular, and the party eventually rallied together (as much as Democrats can) against the war. Moreover, Dean's complaints about the Democratic Party struck such a cord with state party activists that he was able to convert his campaign into a successful race for DNC chair.
In 2008, it is happening on the Republican side now as well. The issue is illegal immigration. In this week's New Yorker, Ryan Lizza explains why the GOP candidates have veered right on immigration: US Rep. Tom Tancredo (R-CO). When he first got to the House about 10 years ago, Tancredo could hardly interest his Republican colleagues on the issue. Now, it is a topic that is discussed in every GOP debate and the subject of attack ads between all the candidates. The issue even tripped up Rep. Hillary Clinton (D-NY), and with her arguably Mayor Rudy Giuliani (R-NYC). Unlike Kucinich or Sen. Mike Gravel (D-AK), Tancredo openly admits he knows he will never be president. But his goal--putting the issue out there and having people agree with his views--has been achieved to a large extent in the GOP primary. Granted, he is the only one who advocated for "bombing Mecca" but even Sen. John McCain (R-AZ)--the author of most of the compromise immigration bills--has reversed course on "amnesty," all thanks to Tancredo.
On the Democratic side this cycle, it has been argued that Sen. John Edwards (D-NC) is pushing Sen. Barack Obama (D-IL) and Clinton to propose much more ambitious health care and energy Independence proposals. Edwards forced Clinton to say she wasn't going to apologize for voting for the Iraq War after he asked Americans for forgiveness. Now Edwards has a real chance still of winning the nomination, which is why the other top contenders have had to address his policy proposals seriously. Still I still can't figure out how he planning on winning New Hampshire or any February 5th state on anything other than momentum.
Other Democratic candidates have similarly impacted the debate. Gov. Bill Richardson (D-NM)--with help from national bloggers like Matt Stoller and Chris Bowers--have made beef with the 'no residual forces' gabit, forcing the top three to first say they would have troops in Iraq until 2013, and now making statements like Obama's pledge to get all American troops out of Iraq by the end of his first year.
Dodd's FISA fight is another example of this. Sen. Chris Dodd (D-CT) knew he really had no chance of becoming president. His initial first goal of running was to rehabilitate his father's reputation. Why else make your campaign book about letters your dad wrote sixty some years ago? But the lack of Senate leadership on constitutional issues like torture, habeas corpus, and wiretapping gave Dodd an opening. He could safely "sacrifice his campaign" by fillibustering bills and offering his own, while calling out Clinton and Obama for never showing up while they campaign.
Some candidates really add nothing to the dialogue. For example, did you know US Rep. Duncan Hunter (R-CA) was running for president? He's running on keeping gays out of the military and building a boarder fence. Those two topics are pretty much covered by the other candidates.
Likewise, Kucinich again is running on the war, this time with added bonus of impeaching Cheney and shaming Congress for lack of action to stop the war. With all of the candidates on the Democratic side against the war, and with no hope of actually impeaching Cheney, he really has nowhere to go. His anti-corporate rhetoric has been overwhelmed by Edwards' populist message too.