by Julian Zelizer

If winning isn`t probable, what else can primary candidates intend to accomplish?

There are a number of things that candidates can achieve for themselves or their parties without actually becoming the nominee.

Selling a message: Often candidates want to make sure that their party colleagues are paying attention to certain issues. They feel that the existing leadership and crop of candidates are ignoring key problems that are central to the health of the nation. There are many people in public life who find this to be enough reason to undertake a serious campaign. This was why Sen. Eugene McCarthy of Minnesota entered the Democratic primaries in 1968, with the goal of making sure that Democrats who opposed the Vietnam War had a seat at the table.

As a political veteran, Sen. Bernie Sanders of Vermont must realize that the odds of defeating Hillary Clinton are slim. Yet regardless of the outcome, he is bringing to the forefront of the party debate concerns about economic inequality, a broken political process and the rapid deterioration of the environment. Even if Sanders doesn`t gain much traction in terms of actual votes, his ability to push Clinton toward dealing more squarely with these problems would be considered a victory.

Mobilizing new constituencies: Sometimes losing politicians help to mobilize new constituencies into the party. Ronald Reagan did this with right-wing Southern conservatives in the 1976 Republican primaries when he challenged President Gerald Ford. Ford defeated Reagan, though barely, but Reagan brought into the party and energized conservatives who ordinarily had not voted in primaries like Texas.

In 2004, Vermont Gov. Howard Dean used pioneering social media technology to attract younger liberals into the Democratic selection process. Although John Kerry won the nomination, only to lose to George W. Bush in the general election, the groups Dean energized would be central to Barack Obama`s 2008 victory.

Among the Republicans in 2015, Sens. Rand Paul and Ted Cruz -- both still long shots for the victory against a Jeb Bush or a Marco Rubio -- have the possibility of reaching libertarian and social conservative Republicans who have become disaffected with the GOP over the past decade. Even if they don`t win, they can bring into the party new groups of voters who can help the GOP in this and other elections, as well as their own future candidacies.

Selling themselves: There are some candidates who get into the primaries these days as a vehicle for their own careers. Donald Trump, the real estate mogul and former reality television star, appears to see the selection contest as a way to advance his own fame and reputation. Running for president has been just another way to keep his name alive in the national media.

Others, like Ben Carson, jump into the contest without a clear agenda or connection to broader groups. Their goal seems to be a desire to elevate their own role in the public arena. With such a vibrant world of political media, consulting and think tanks, running for president can enhance a person`s stature and offer opportunities. Mike Huckabee earned himself a spot on Fox News after previous runs.

With Trump, one lure may be that he has name recognition and can likely get into the first GOP debate (on Fox, limited to 10 candidates) and the first tier of the first CNN debate (the network will have a second debate for those who don`t make the first cut). That is priceless national exposure.

Another big outcome of a presidential run could be a vice presidential or Cabinet slot, and this must be on the minds of some of the longer shots. The visibility and stature that can come from running could enhance the appeal of a future appointment of someone like Pataki or Chris Christie.

Testing the waters: For many other candidates, it is clear that winning in American politics can take several tries. Entering the primaries and caucuses is a learning experience. When Mitt Romney ran in 2008, he believed that he had a good chance for the nomination. But even when he lost, the experience helped him be a stronger candidate in 2012, when he won the nomination. Running is also an effort to solidify the credentials needed to approach campaign contributors and super PACs in future years with the hope of being a credible candidate.

There are lower-key candidates, like John Kasich, Scott Walker, and Martin O`Malley, who have high aspirations in the near future but also realize that getting through the competition in 2016 can make them stronger for the next time around.

The primaries and caucuses continue to serve as a powerful national forum through which to achieve a large number of goals. Particularly in an age when there is so much politically centered media, constantly covering the endless campaign and giving attention to any candidate who enters, and when super PACs can single-handedly finance campaigns, the temptations to declare for the presidency are stronger than ever.

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