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.

(Zoeann Murphy/The Washington Post)

[Blame game: Trump casts immigrants as dangerous criminals, but the evidence shows otherwise]

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 to check off the president’s immigration promises.

Most notably, Trump signed an executive order during his first week in office that, among other things, vastly expanded the pool of the nation’s 11 million illegal immigrants who are deemed priorities for deportation.

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Deportations had fallen sharply in the final years of the Obama administration as the former president tightened enforcement guidelines to focus on hardened criminals. But under Trump, Immigration and Customs Enforcement has begun to ramp up the number of immigrants who are being placed in removal proceedings.

Federal agents arrested 21,362 immigrants, mostly convicted criminals, from January through mid-March, compared with 16,104 during the same period last year, according to federal data. Arrests of immigrants with no criminal records more than doubled, to 5,441 in that period.

“This is the Trump era. Progress is being made daily, and it will continue,” declared Attorney General Jeff Sessions, who has begun to reorganize the Justice Department to prosecute more immigration cases. “This will be the administration that fully enforces our nation’s immigration laws.”

Mark Krikorian, executive director of the Center for Immigration Studies, which advocates for lower immigration levels, called Trump’s first few months a “mixed picture,” but he said the administration “has clearly made some progress.”

“The decline at the border is not something that happened on its own — it’s a reaction to concerns Trump is going to restore the enforcement of immigration laws,” Krikorian said. “It won’t last if that fear isn’t realized, but if it is, if Trump follows through, we’re likely to see a sustained reduction in border crossings.”

The question is how successfully the administration can translate the tougher talk into sustainable policies.

[Trump administration moving quickly to build up nationwide deportation force]

Internal planning documents from the Department of Homeland Security leaked recently showed that the agency is preparing to significantly ramp up the nationwide deportation force that Trump promised on the campaign trail.

The agency has secured 33,000 additional detention beds and is considering waiving some requirements, including a polygraph exam and a physical fitness test, to speed up the hiring of more immigration agents. ICE and CBP also are working with dozens of local police departments interested in being more deeply involved in immigration enforcement.

But the administration’s boldest actions have been blocked by the courts, including Trump’s attempted temporary freeze on the nation’s refu­gee program, the entry ban targeting majority-Muslim countries and the administration’s attempts to withhold some federal funds from sanctuary cities that do not cooperate with federal immigration authorities.

And like President Barack Obama before him, Trump has struggled to deport some foreign-born criminals whose home countries refuse to take them back.

“The administration is doing a good job signaling to the rest of the world they will be cracking down on abuses of the illegal immigration system,” said Leon Fresco, an immigration attorney who previously served in the Obama Justice Department and as an aide to Sen. Charles E. Schumer (D-N.Y.). “That should be the point without needing to create the excesses of the travel ban. There is a balance that can be reached if this administration simply signals it will be enforcing immigration law that does not need to be unduly draconian in a way that is not permitted by law.”

Immigrant rights advocates point to the lessons learned from legal battles in recent years in several states, including Arizona and Alabama, that enacted laws granting local police broad powers to arrest and imprison immigrants. Most of those laws were gutted or struck down by federal courts.

“What they’ve done is to export the failed enforcement strategy from the state level that was anti-immigrant to the national level,” said Marielena Hincapié, executive director of the National Immigration Law Center.

The goal is to “make life so impossible and difficult for people that they would self-deport,” Hincapié said. “That’s not the case. People just went underground. Here, a big part of the strategy is to instill fear and create a chilling effect.”

Trump is unlikely to back off from his approach, and the administration has found ways to slow the flow of immigrants despite legal setbacks. The number of refugees entering the United States has plummeted from nearly 10,000 last October to fewer than 2,500 in April.

Immigration hawks have also continued to press the White House to do more, including overturning a deferred action program started under Obama that has granted work visas to more than 700,000 “dreamers” who arrived illegally when they were children. Although he promised to overturn the program on Day One, Trump has yet to end it.

But just over three months into Trump’s tenure, the frame of the political debate over immigration policy has begun to shift.

“One thing this administration has done that the Democrats’ message has to recalibrate for is that it’s not credible to the American people to say enforcement plays no role in [reducing] the numbers of immigrants coming illegally,” Fresco said. “Some have tried to perpetuate a myth that it is not linked. To the extent the numbers stay low, one thing the Trump administration has been able to say that is a correct statement is that enforcement does factor into the calculus.”

Devlin Barrett contributed to this report.