For some reason, we normally stop talking about caucuses vs. primaries after Iowa, but there are others. In theory, you might not assume that the different way states choose candidates should favor a particular campaign, but it often does. In 2008, for example, Obama showed a lot more success in winning caucuses than primaries, which gave him a big advantage in winning the nomination. Caucuses tend to favor candidates who have better organizations, who can get all of their voters to a particular voting site at a specific time.
Among the many odd things about this election has been that Donald Trump has been running his campaign with virtually no organization. He didn't hire people to work in particular key districts, staff offices with large numbers of volunteers, and knock on doors to distribute literature. This played a critical role in his losing the Iowa caucus, but we stopped discussing it after he nonetheless won decisively the Nevada caucus. But Nevada has always been a particularly strong state for him, as he even influenced the 2012 election there for Romney.
Three days ago, eleven states voted for the Republican candidates; nine used primaries, and two used caucuses. Of the nine primary states, Trump won seven, losing only Oklahoma and Texas to Ted Cruz, the Senator from Texas. Of the two caucuses, he lost both Alaska and Minnesota, the latter finishing in 3rd place.
Why might that matter? Well, tomorrow, four more states are voting for the Republican nomination. Except only one (Louisiana) will be using a primary, while three (Kansas, Kentucky, and Maine) will be using caucuses. Three days later, there will be two more caucuses in Idaho and Hawaii along with primaries in the much bigger states of Michigan and Mississippi.
States aren't the only geographic entities to choose nominees either. On March 6th, Puerto Rico will decide where its 23 delegates go using a primary, but on March 12th, Washington DC and Guam will both be holding their elections for their 28 delegates combined using caucuses.
We're right now in this interesting moment in the Republican nomination battle, where Trump has been losing bits of momentum under attack from investigative journalists to Mitt Romney, in the lead-up to March 15th, when the election rules change dramatically, and delegates are no longer distributed proportionally, but rather as winner-takes-all, a massive advantage to a candidate who can win states in bunches. The next ten days are therefore remarkably significant as they will suggest who has the momentum going into this pivot point of the campaign. They'll tell us if Trump can continue to win states at his current rate, and if not, who is the best bet to beat him. Over those ten days, eight states will vote, and five of them will be using a voting method that distinctly disfavors Donald Trump.