The report's findings challenge depictions of the U.S. border as a place where American law enforcement is overwhelmed and ineffective. President Trump has ordered DHS to make preparations for the construction of a wall between the United States and Mexico, and last week he met with Democratic Party leaders to negotiate additional border security improvements.
The new DHS report indicates the agency has already made significant progress in its ability to stop people from sneaking in or consider trying. Arrests along the Mexico border fell to historic lows during the Obama presidency, then dropped further after Trump took office vowing a crackdown.
"Available data indicate that the southwest land border is more difficult to illegally cross today than ever before," the report states, while noting that the number of arrests made by U.S. agents is at its lowest point since 2000, "and likely since the early 1970s."
Efforts to gauge the flow of illegal immigration to the United States are often just as politicized as the issue itself, but Congress has instructed DHS to produce detailed reports on the current state of U.S. border security and the effectiveness of American agents' ability to stop illegal immigration.
In the past border security has been typically measured by fluctuations in the number of "apprehensions," or arrests made by U.S. agents along the border.
But advocates of tougher border enforcement say counting arrest totals do not effectively measure security, because they cannot quantify the number of migrants who succeed at getting in or successfully evade capture by returning to Mexico, where U.S. law enforcement can't pursue them.
The new report attempts to take those factors into account by combining arrest totals ("apprehensions") with the number of border crossers who are turned back ("interdictions"). It also includes the number of people considered "got aways," who are individuals that U.S. agents observe making a successful illegal entry.
The department has made even bigger improvements in its ability to discourage and deter migrants from making repeated attempts to cross, a category known as "recidivism," the report states. In previous decades, just 10 to 40 percent of illegal border crossers gave up after their first attempt ended in an arrest. Today that figure is as high as 75 percent, the report said.
Another sign of the difficulty, DHS notes, is the increase in smugglers' fees, which have jumped "from a few hundred dollars in the 1980s to almost $4,000 today, accounting for inflation."
The number of U.S. agents assigned to the Mexico border has nearly doubled since 2004, and Trump has called for 5,000 additional officers. But falling numbers of would-be migrants mean there have been fewer suspects for them to arrest. Last year the U.S. Border Patrol made about 20 arrests per officer, leaving many to go days or weeks without taking anyone into custody.
"There are agents in El Paso who go a whole month without making a single arrest," said Adam Isacson, a border security expert at the Washington Office on Latin America, which advocates for migrant rights.
"We have never seen monthly totals so low," Isacson said. "We're simply not dealing with a flood of migrants."
In the report, DHS said it does not believe the falling arrest numbers could be a sign of the agency's diminishing effectiveness. It notes the number of "got-aways" observed by Border Patrol agents has declined from 615,000 in 2006 to 106,000 last year, a drop of 83 percent.