History shows that when the major party nominees for president have not cleared the field of notable challengers before summer, they tend to lose in the fall.
Donald Trump's decisive victory in the New Hampshire primary puts him on a clear path to securing the Republican nomination. It is also likely to fuel calls for Nikki Haley to drop out of the race.
The former governor of New Jersey - and onetime Trump ally - announced the end of his campaign at a town hall in Windham, N.H., Wednesday, just days before the first in the nation Iowa caucuses.
The presidential nominating contests kick off with voting in Iowa on Jan. 15. That's followed by New Hampshire on Jan. 23. Here are some more key dates for this year's election calendar.
The former South Carolina governor has been performing better than expected in recent early-state primary polls, but still lags far behind former President Donald Trump.
Elections are becoming more expensive as candidates vie for voters' attention. But there are strict rules about how money is raised, how it can be used and how to prove you're following the laws.
Ramaswamy has pitched himself as a younger, more extreme version of the former president. While he's gained in the polls, a GOP strategist warns "he'll never surpass Trump by trying to mimic Trump."
Former President Donald Trump skipped the debate and turned himself into Georgia police this week. Still, he's way ahead of his primary opponents and coasting toward the nomination.
How far could a president go to stay in office if convinced his re-election was crucial to the nation? What liability would he face? And how much stress can the fragile structure of democracy stand?
The Republican presidential field is the most diverse it has ever been, raising questions about race, identity and immigration for candidates of color in an overwhelmingly white party.