This Oct. 19, 2018 frame grab from video provided by Televisa, shows migrants bound for the U.S.-Mexico border waiting on a bridge that stretches over the Suchiate River, connecting Guatemala and Mexico, in Tecun Uman, Guatemala. The gated entry into Mexico via the bridge has been closed. The U.S. president has made it clear to Mexico that he is monitoring its response. On Thursday he threatened to close the U.S. border if Mexico didn't stop the caravan. (Televisa via AP)