The GOP presidential field for 2016 may be the largest-ever in either party, with eight formally-declared candidates and another eight widely expected to enter the race in the next few months. Here are seven reasons why there are so many Republicans seeking the White House:
1. The Fame Game
To put it simply, running for president can make a person famous, rich, deeply influential or all three, even if they lose. Former Arkansas Gov. Mike Huckabee was a serious candidate during his 2008 run, winning eight states. It's unlikely he entered the race simply to gain fame.
But his unsuccessful campaign helped him get a show on Fox News. It's hard to imagine he would have received such an opportunity without having run for president and become a favorite of the most conservative Republicans.
After his unsuccessful campaign in 2012, Rick Santorum was tapped to run a company that makes Christian-themed movies. Herman Cain was a virtually unknown former businessman who is now popular among conservative activists after his campaign four years ago.
Sarah Palin didn't actually run for president, but she's perhaps the perfect example of how a national campaign can change a politician's life. Her vice-presidential run turned into a book deal, a tv show and both fame and money that she never could have achieved as governor of Alaska. (Test: Do you know the name of the current governor of Alaska?)
She also, at least for a time, gained major sway within the Republican Party. Candidates wanted her endorsement and for Palin to campaign with them.
It's hard to determine the motives of any individual politician. That said, Ben Carson fits the fame incentives perfectly. He's already drawn a huge amount of attention to himself through his candidacy that could help him sell books and appear on FOX News for years after his 2016 run.
Carly Fiorina and Donald Trump are both already famous and wealthy from their time in the business world. But presidential candidacies give them a chance for influence in a different realm. Fiorina in particular is increasing her chances of being appointed to the Cabinet of the next Republican president.
The national spotlight does sometimes hurt a politician. In 2011, Rick Perry was on his way to finishing what was considered a strong tenure as governor of Texas. Then, he opted to run for president and became a national laughingstock, unable in a debate to recall the three government agencies he was promising to close if elected president.
Perry though has a ready-made solution: a second campaign. Running for president can serve as a kind of redemption tour for politicians, even if they don't win.
Rick Santorum had been effectively forced out of politics, losing by more than 17 points during his 2006 reelection race in Pennsylvania. His long-shot presidential run in 2012 reinvigorated his political life.
Former New York Gov. George Pataki, who left that office in 2007, could be a more important figure in Republican politics through his presidential campaign, even though he is almost certain to lose. New Jersey Gov. Chris Christie could use his campaign to distance himself from the "Bridgegate" scandal.
3. Barack Obama
For senators like Ted Cruz, Rand Paul and Marco Rubio in particular, the Obama example is hard to ignore. In the past, the presidential field was usually composed of sitting or former vice-presidents and then senators or governors who had already served at least one term in office. George W. Bush won reelection as governor of Texas in 1998, then started running for president. John Kerry had been a long-term senator from Massachusetts.
Obama had barely served two years in the Senate before opting to run for president in 2008. And he won. So Cruz, Paul and Rubio are in effect making the same case Obama did seven years ago: the time for my leadership and vision is now, and I can't lead from the Senate.
4. No Incumbent president
Obama is relevant in another way. In 2008, like in 2016, there is no incumbent president or sitting vice-president in the field. In 2012, even as Republicans dismissed Obama as a failed president, many potential candidates were wary of running against him, aware of the advantages incumbent presidents have.
Hillary Clinton is almost like a sitting vice-president, since the Democratic Party is mobilized around her and she is facing no strong challenger in the primary. But winning the third straight term for the same party is much harder than a president going for reelection.
The Republican nominee will have a very strong chance of being elected president by simply running as a change candidate and arguing the country does not need a third term of Obama-like policies.
Rubio is young, so he could have waited to run for president. But what Obama showed in 2008 was that running at the right time can overcome a lack of experience. In 2020, a Republican could have won in 2016, so Rubio would have to wait out that person's tenure. Or Clinton or another Democrat would be president, forcing Rubio to face the power of incumbency.
5. No Strong Front-Runner
Hillary Clinton's strength is keeping other Democrats out of the race. On the Republican side, over the first five months of the campaign, a trio of front-runners have emerged: Jeb Bush, Marco Rubio and Scott Walker.
But they all have potential flaws. Bush is more moderate on issues like immigration than many GOP activists, and some conservatives were turned off by his father and brother's presidencies and are wary of a third Bush tenure. Rubio is a first-term senator and co-wrote a bill that would have granted citizenship to undocumented immigrants. Walker is untested on the national stage and made some mistakes early on, like non-answering when asked if Obama is a Christian.
The weakness of the front-runners is drawing into the race candidates, like Ohio Gov. John Kasich, who see a path to victory if those three flounder.
6. The Rise of Super PAC's
In the days when a candidate could only raise money in $2000 increments, it would have been hard for Rubio to run. He is not personally rich, and much of the GOP establishment who might have otherwise backed him instead went for Bush.
But with a few mega-donors bankrolling his super PAC, Rubio may be outspent by Bush, but the senator can raise enough to be a credible candidate.
Being able to raise money in unlimited amounts also helps someone like Kasich who has entered the race so late.
7. The Republican Party is Very Divided on Policy
Some of the Republican candidates have very strong, distinct views of policy that they feel uniquely qualified to advocate. Bush, Rubio and Kasich all want to create a kind of post-Tea Party GOP that is more focused on offering conservative policy solutions than shrinking the size of government.
Paul is pushing to reduce the size and scope of the U.S. government's footprint both at home and abroad. His policy views, from winding down the war on drugs to limiting national security surveillance programs, would be a sharp contrast to much of the Republican Party's current ideology. On some issues, if Paul were not running, no other candidate would be expressing these views.
Huckabee and Santorum want the Republican Party to shift away from its close alliance with big business. They are more skeptical about the benefits of immigration and free trade than the rest of the field.
Walker and Cruz are deeply conservative on nearly every issue and want to push the country in that direction. Their presidencies would likely include deep cuts to programs like Medicaid and food stamps, pushes to weaken the power of labor unions, more limits on abortion rights and the appointments of strong conservatives as federal judges.
Bush, Kasich and Rubio are pitching a more efficient and effective version of George W. Bush's conservatism. Electing Walker or Cruz would likely result in policies much closer to that of Tea Party activists and House Republicans.