President Trump tweeted Monday morning that the United States will begin slashing foreign aid to Central American countries including Guatemala, Honduras and El Salvador, after they were "not able to do the job of stopping people from leaving their country" and joining a caravan of thousands headed towards the U.S.

Mr. Trump, who has for days now blasted Democrats and the United States' immigration laws over the caravan, also warned, without citing evidence, that "unknown Middle Easterners" and "criminals" are mixed into the caravan of people heading towards the United States' southern border. The president declared on Twitter he has alerted the U.S. Customs and Border Protection and the U.S. military "that this is a national" emergency.

"Guatemala, Honduras and El Salvador were not able to do the job of stopping people from leaving their country and coming illegally to the U.S.," Mr. Trump tweeted Monday. "We will now begin cutting off, or substantially reducing, the massive foreign aid routinely given to them."

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Mr. Trump has for days threatened to cut off aid to the Central American countries if they fail to stop residents from pouring into the United States. The president has also criticized Mexico for failing to stop the crowd.

"Sadly, it looks like Mexico's Police and Military are unable to stop the Caravan heading to the Southern Border of the United States," the president tweeted moments earlier. "Criminals and unknown Middle Easterners are mixed in. I have alerted Border Patrol and Military that this is a National Emergy. Must change laws!"

The president, asked on the White House South Lawn Monday afternoon if there are terrorists in the caravan, told a journalist to go into the middle of the caravan and take his camera.

"You know what you should do john, go into the middle of the caravan, take your camera and search," the president said. "No no, Jon, take your camera, go into the middle, and search. You're going to find MS-13, you're going to find Middle Eastern, you're going to find everything. And guess what, we're not allowing them in our country."

Mr. Trump has openly described the caravan and border crisis a great issue for Republicans politically ahead of next month's midterms. Mr. Trump has repeatedly claimed the Democrats don't care about security or law and order, particularly when it comes to immigration. The president has threatened to seal off the U.S.-Mexico border entirely, if necessary. Many of the migrants hail from Honduras, fleeing violence, poverty and a lack of jobs.

"Every time you see a Caravan, or people illegally coming, or attempting to come, into our Country illegally, think of and blame the Democrats for not giving us the votes to change our pathetic Immigration Laws! Remember the Midterms!" Mr. Trump also tweeted Monday morning. "So unfair to those who come in legally."

The president is campaigning in the border state of Texas Monday night for former rival Sen. Ted Cruz, where he is expected to slam Democrats and Cruz' opponent Rep. Beto O'Rourke as weak on immigration.