Nobody has presented any evidence that there are people from the Middle East in the migrant caravan. 
As is frequently the case whenever Trump says anything new before 9 a.m., this "Middle Easterners" tweet appears to have been inspired by Fox and Friends.
Follow the bouncing ball: 1) Guatemala's president said at a conference that they had arrested, over some period, 100 people linked to terror. Completely unrelated to the caravan. 2) Right-wing sites used that to raise caravan fears. 3) Fox joined in. 4) The president joined in.
