Coupled with the caravan, Trump administration officials have said it's a full-on crisis. They say loopholes in laws have allowed for a worsening border crisis where the vast majority of people coming illegally to the U.S. cannot be easily returned home.
But the administration's efforts to enforce a hard-line stance on immigration through regulation changes and executive orders have been largely thwarted by the court system and, in the case of family separations earlier this year, stymied by a global outcry that prompted Trump to scrap separations through an executive order June 20.
While such caravans have occurred semiregularly over the years, this one has become a hot topic ahead of the Nov. 6 midterm elections. The march appeared to begin as a group of about 160 who decided to band together in Honduras for protection against the gangs who prey on migrants travelling alone and snowballed as the group moved north.
If they arrive, they are likely to face long lines at ports of entry. Family detention space is limited to about 3,300 beds nationally, and, under a court settlement, children can generally be held no more than 20 days, so many would likely be released.
In a letter to the Department of Homeland Security and the State Department on Tuesday, Senate Judiciary Chairman Chuck Grassley and Sen. Mike Lee suggested that the administration make a "third party" agreement with Mexico that would force any caravan members seeking asylum to do so in their country of arrival — Mexico. The Republican lawmakers said the process already works that way in Europe.
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." He said he had alerted Border Patrol and the military and called for a change in laws, and said that people of Middle Eastern descent had joined the group.
He later acknowledged that his claim was only a hunch.
"They could very well be," he said. "There's no proof of anything. But there could very well be."
Asked if he was implying there were terrorists in the caravan, Trump said, "There could very well be."
Tyler Houlton, a spokesman for Homeland Security, later tweeted that the department could confirm that gang members or serious criminals are in the caravan, but he didn't provide details.
It was the latest effort to thrust immigration politics into the national conversation in the closing weeks of the congressional elections. He and his senior aides have long believed the issue — which was a centerpiece of his winning presidential campaign — is key to motivating GOP voters to turn out.
"Blame the Democrats," he wrote. "Remember the midterms."