Over the past month, the crowded Republican presidential primary field saw its first two casualties: former Texas governor Rick Perry and Wisconsin Gov. Scott Walker. These early exits surprised some. Walker was as an early front-runner in the polls owing to his conservative record and ability to win statewide office in a traditionally blue state. Perry was seen as a dark horse with untapped potential.
So who's next? While it's impossible to predict, based on previous research by me and several colleagues, I think Govs. Chris Christie and John Kasich are in danger of dropping out. Here's why.
My colleagues and I studied the 2000 GOP primary, which also featured a large group of candidates. There was no clear front-runner as the campaign began but Gov. George W. Bush quickly became the establishment candidate. Although Sen. John McCain won the New Hampshire primary, Bush won in South Carolina and regained momentum. Other candidates included John Kasich, then a member of the House of Representatives, political commentator Pat Buchanan, former labor secretary Elizabeth Dole, and self-funded businessman Steve Forbes.
We looked at which factors over the course of the campaign helped candidates stay in longer or drop out of the race. We found that early in the campaign, during the "invisible primary," positive news coverage plays an independent role above and beyond fundraising or polling. But after the primaries begin, polling relative to the front-runner becomes more important, and media and money matter less.
Media and money also matter differently depending on the candidate. Money is important to "big shot" candidates - those doing relatively well in the polls - but news coverage is important to "long shots" early in the race. Finally, we also found that candidates running more of a policy- or issue-focused campaign may stay in longer than expected.
Of course, 2016 is not 2000. In particular, the GOP has done far less to coordinate around a candidate this cycle than it did around Bush in 2000. But we can still learn some things from our previous study.
For one, Jeb Bush seems to fit our findings. He is a "big shot" with a lot of money, but not polling exceptionally well or generating a ton of positive media coverage. Bush has enough money to keep his campaign running until later when the importance of media coverage matters less and delegates start to add up.
Similarly, candidates whose campaign is more centered on a particular policy agenda - such as former governor Mike Huckabee, former senator Rick Santorum, and possibly Sen. Rand Paul, too - may prove more likely to stay in the race when other factors suggest they should drop out. They can adopt a survival strategy of specialization and continue to campaign with limited resources.
Outsider candidates, such as Donald Trump, Ben Carson and Carly Fiorina, should be considered "big shots" due to their relatively strong poll numbers. This means media coverage has little influence on the chance they will drop out early, as long as they remain competitive in the polls and have sufficient funds. But if they do fade in the polls as the primaries begin, they will be more likely to drop out, even though they can self-fund to keep their campaigns going.
So what about Christie and Kasich? Their main problem is that it has been hard to break through and get substantial positive media coverage early in the campaign. And, similar to Perry and Walker, Christie and Kasich are career politicians who still see a future in Republican circles. Staying in too long may hurt them in the future.
On the other hand, if Christie, Kasich, and the other "career politician" candidates assume that outsiders like Trump or Carson won't win the nomination, then perhaps it gives these candidates a reason to stick it out as long as possible - waiting for something to happen so that they can move up.
Another major difference in 2016 is the prevalence of super PACs. Unlike in 2000, even one wealthy donor can help keep a candidate in the race. Given the behavior of these donors in the past - and given that super PAC support didn't keep Walker or Perry in the race - it is difficult to predict who will benefit this time around.
Of course, we are still a few months away from an actual primary or caucus, so there is plenty of time for a new front-runner to emerge and transform the state of play.