President Donald Trump on Monday escalated his attacks on the caravan of migrants making their way to the United States from Central America, calling the situation a national emergency and declaring without evidence that "Criminals and unknown Middle Easterners are mixed in."

"I have alerted Border Patrol and Military that this is a National Emergy," the president wrote in the first of a series of Twitter posts about the caravan, apparently misspelling the word "emergency."

Trump also said that his administration would begin to cut off or reduce foreign aid to Guatemala, Honduras and El Salvador. He said the three nations "were not able to do the job of stopping people from leaving their country."

The White House did not respond to a request for more details about the president's posts, and it's unclear if he would have the authority to carry out the threats without approval from lawmakers.

The president has the power to formally declare a national emergency under the National Emergencies Act but is required to follow formal procedures, and it is not clear if he has done so.

Congress has softened some of the president's previous demands to reduce U.S. foreign aid. The president's attempt to cut foreign aid in this year's budget was ultimately rebuffed by lawmakers. The administration then attempted to avoid spending the money allocated for foreign aid using a so-called "rescission" package, Reuters reported, but later dropped the plan.

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The president, who has made restrictive immigration a key campaign issue as well as a signature aspect of his foreign policy, again on Monday raised the specter of involving the U.S. military to halt the entrance of the migrants and redoubled his call to "change laws."

"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! So unfair to those who come in legally," Trump wrote.

The president has sought to make immigration a decisive issue in the upcoming November midterms and has leveraged the image of the migrant caravan while campaigning around the country in order to do so. Immigration remains a key issue for GOP voters, consistently polling alongside jobs and the economy as the most important issue for Republicans.

The president's Monday morning tweets mirror comments he made last week. On Thursday, the president wrote in a tweet that he would "in the strongest of terms, ask Mexico to stop this onslaught - and if unable to do so I will call up the U.S. Military and CLOSE OUR SOUTHERN BORDER!"

Trump campaigned for the presidency on an "America First" foreign policy platform and infamously launched his bid by claiming that Mexico was sending criminals, including murderers and rapists, into the United States. In April, at an event that was nominally about celebrating the Republican tax bill, the president referred back to his false claim.

"Everybody said, oh, he was so tough. I used the word rape," Trump said.

Since he took office, critics have called out as racist some of the president's immigration policies, particularly around the implementation of his controversial Muslim "travel ban." The Supreme Court upheld a version of the ban, which restricts immigration to the U.S. from a number of Muslim-majority countries, in a blockbuster ruling last term.

In January, the president reportedly railed against immigrants from African nations, Haiti and El Salvador in a meeting in the Oval Office.

"Why are we having all these people from s---hole countries come here?" Trump asked, according to The Washington Post. Trump, who denied using such harsh language, reportedly said the U.S. should have more immigrants from countries like Norway.

A spokesperson for the U.N. human rights office said of the remarks at the time that "there's no other word one can use but racist."

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