A Border Patrol agent on duty at the fence between the United States and Mexico in San Ysidro, Calif., in mid-April. Apprehensions of people trying to enter the United States illegally along the southern border have plummeted, according to federal data. (Sandy Huffaker/Getty Images)

In many ways, President Trump’s attempts to implement his hard-line immigration policies have not gone very well in his first three months. His travel ban aimed at some Muslim-majority countries has been blocked by the courts, his U.S.-Mexico border wall has gone nowhere in Congress, and he has retreated, at least for now, on his vow to target illegal immigrants brought here as children.

But one strategy that seems to be working well is fear. The number of migrants, legal and illegal, crossing into the United States has dropped markedly since Trump took office, while recent declines in the number of deportations have been reversed.

Many experts on both sides of the immigration debate attribute at least part of this shift to the use of sharp, unwelcoming rhetoric by Trump and his aides, as well as the administration’s showy use of enforcement raids and public spotlighting of crimes committed by immigrants. The tactics were aimed at sending a political message to those in the country illegally or those thinking about trying to come.

“The world is getting the message,” Trump said last week during a speech at the National Rifle Association leadership forum in Atlanta. “They know our border is no longer open to illegal immigration, and if they try to break in you’ll be caught and you’ll be returned to your home. You’re not staying any longer. If you keep coming back illegally after deportation, you’ll be arrested and prosecuted and put behind bars. Otherwise it will never end.”

The most vivid evidence that Trump’s tactics have had an effect has come at the southern border with Mexico, where the number of apprehensions made by Customs and Border Patrol agents plummeted from more than 40,000 per month at the end of 2016 to just 12,193 in March, according to federal data.

A U.S. Border Patrol agent patrols along the U.S. Mexico border area in San Diego, Calif. (Mike Blake/Reuters)

Immigrant rights advocates and restrictionist groups said there is little doubt that the Trump administration’s tough talk has had impact.

“The bottom line is that they have entirely changed the narrative around immigration,” said Doris Meissner, who served as the commissioner of the U.S. Immigration and Naturalization Service in the Clinton administration. “The result of that is that, yes, you can call it words and rhetoric, and it certainly is, but it is changing behavior. It is changing the way the United States is viewed around the world, as well as the way we’re talking about and reacting to immigration within the country.”

Experts emphasized that it is still early and that the initial success the administration has had in slashing illegal border crossings could be reversed if it fails to follow through on more aggressive enforcement actions that will require more than just rhetorical bombast.

Many of the other initiatives Trump has called for — including additional detention centers and thousands of new Border Patrol officers and immigration agents — are costly. Others, such as his vow to withhold federal funds from “sanctuary cities” that protect immigrants, are facing legal challenges.

Yet unlike areas such as trade, health care or foreign policy, where Trump has moderated his extreme campaign positions or failed to advance his agenda, the administration has systematically sought…