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President Donald Trump has taken to Twitter scores of times since taking office to offer his opinion on everything from the size of the crowd at his inauguration to his view that the Mueller probe is a witch hunt.

Now, he has used the platform to declare a national emergency, citing one of his favorite subjects, which is what he sees as armies of people crossing the Mexican border. He likely believes the problem is great enough to get support for his border wall.

Trump tweeted:

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

— Donald J. Trump (@realDonaldTrump) October 22, 2018

Mexico sent two planeloads of soldiers to stop thousands of people crossing its southern border with Guatemala. Some have even dropped into the Suchiate River, which separates the two countries, in an effort to dodge border patrols. The federal troops ballooned to 700. Estimates put the swell of migrants at 5,000 to 9,000. Many have sweltered on a bridge between the two countries. Mexico has opened camps where the migrants can get food and water. However, what will happen to them is still an open question.

Immigration from people across the Mexican border is one of Trump’s primary issues. He has promised the American people to block the flow with a border wall. Estimates for building the wall are into the hundreds of billions of dollars. And a number of experts question whether a wall along the 2,650 miles can be effective.

The immigration problem has been worsened as people from Central America tried to reach the United States via Mexico. Mexico has threatened to deport people back to their countries.

Over the weekend, Trump said in a tweet what he believes should be the next step, which is that the Mexicans grant the immigrants asylum. “If they fail to do that, the U.S. will turn them away.”