How many caravans are coming?

Four distinct caravans, with as many as 10,000 total members, have set out for the United States, according to Alex Mensing, a project coordinator with Pueblo Sin Fronteras, a transnational group that organized the migrant caravan that captured Mr. Trump’s attention last spring.

But the groups have splintered and shape-shifted in the face of grueling travel, government opposition and the opportunity to seek asylum in places other than the United States.

Mr. Mensing said that the majority of the caravan members were from Honduras, with others coming from El Salvador, Guatemala, Nicaragua and Costa Rica. He also said that new caravans were beginning to form as recently as a few days ago, originating in El Salvador.