MEXICO CITY (Reuters) - Last month’s 40 percent decline in migrant detentions along the southern U.S. border represents a victory for U.S. President Donald Trump, but may prove short-lived unless he follows through with his hard-line vows, past experience shows.

FILE PHOTO: A U.S. worker inspects a section of the U.S.-Mexico border wall at Sunland Park, U.S. opposite the Mexican border city of Ciudad Juarez, Mexico, November 9, 2016. Picture taken from the Mexico side of the U.S.-Mexico border. REUTERS/Jose Luis Gonzalez/File photo

Trump’s administration on Wednesday trumpeted the February decline as evidence its executive orders on immigration were working, fulfilling his promise to crush illegal migration.

But an analysis of recent U.S. apprehension data, along with interviews with migrants, diplomats and activists, suggests peoples’ fears will subside if Trump fails to realize his tough policies, causing the flow to rise.

“Right now, nobody wants to go” to the United States, said Victoria Cordova, who along with her daughter Genesis, was part of the first group of mothers and children deported by plane from the United States to Honduras in 2014.

“If in the future the situation looks better, well, I imagine then people will be more willing to travel.”

The number of apprehensions rose drastically in March 2014, in what mushroomed into a major crisis of unaccompanied minors for the Obama administration.

Finding the border infrastructure overwhelmed by the flow, the Obama administration funded advertisements in Central America urging people to stay at home, leaned on Mexico to intercept more migrants, and deported mothers and children in a handful of high-profile flights.

The move worked: There were 68,804 apprehensions in May 2014 and only 34,003 in September, the last month of that fiscal year.

For most of 2015, the numbers of apprehensions remained low. However, there were only ever a sprinkling of flights with mothers and children, and smugglers and migrants soon realized the United States was only acting tough.

An immigration backlog meant many people could remain for months before their case was heard, while a 2015 federal court decision limiting the time mothers and children could be detained created the impression they could stay.

Throughout the latter half of 2015, apprehensions rose.

In January 2016, the Obama administration carried out multiple deportation raids, which led to a fresh drop in apprehensions.

By March, though, the effects had worn off, as people smugglers urged migrants to migrate before Trump’s border wall went up.

In November 2016, when Trump won the election, 63,367 people were apprehended, before the numbers fell off as many fretted about the repercussions of his victory.

During his confirmation hearings, and on a trip last month to Guatemala, U.S. Homeland Security Secretary John Kelly focused on deterrence, emphasizing the point this week by saying he might separate mothers and children on the southern border.

“I believe that perceptions of a lack of enforcement can increase the flow of people attempting to enter the United States illegally,” he said in January, responding to a Senate committee’s pre-hearing questions.

So far, his message seems to be resonating in Central America, but it is unclear for how long.

“People may be pausing for a month or two and waiting to see how much of what’s being said in rhetoric actually starts to happen,” said migration expert Maureen Meyer.

Click bit.ly/2mcibSX for graphic on Central American migration to the U.S.