Migrant shelters along the southern border are filling up again. Immigration lawyers in the region say their caseloads are spiking. Across the Southwest, border officers are stopping more than 1,000 people a day.

Just months after border apprehensions hit a 17-year low, which administration officials proudly celebrated as a “Trump effect,’’ the number of migrants trying to enter the United States has been surging, surpassing 40,000 along the Southwest border last month, more than double the springtime numbers, according to new data from the Homeland Security Department.

Many factors, including the Central American economy and gang violence, play a role in migration patterns. But it also appears that any deterrent effect of President Trump’s tough talk and ramped-up immigration enforcement has begun to wane.

In interviews, volunteers and lawyers along the border say that migrants and smugglers have stopped lying low, deciding that trying to get a foothold in a well-off and safe country was no riskier than in the past.

“I think this was a ‘Let’s wait and see what’s going to happen’ period,’’ said Ruben Garcia, director of the Annunciation House, a shelter in El Paso, Texas, that provides housing to recent border crossers as they search for more permanent places to live.

Garcia pointed to the president’s plan to hire tens of thousands of border agents, which was announced in February but has yet to come to fruition because Congress still has not provided the funding. The same is true for Trump’s centerpiece project, the border wall.

“After it became evident that there wasn’t a dramatic change on the part of the administration, then the smugglers started selling their product again and the flow began to resume,’’ Garcia said.

In releasing the data, the administration acknowledged that it had lost ground in its effort to stem immigration. But it also seized on the statistics to make the case that Congress should overhaul immigration laws to deter more people from coming.

The Trump administration and Republicans in Congress have been seeking new border security measures in exchange for permitting 800,000 young immigrants in the country illegally to remain in the United States. On Tuesday, the president indicated he would even consider allowing millions more immigrants to remain in the country, provided Congress took steps to keep new ones from entering.

The numbers of apprehensions are an indication of border activity, but they do not count those who slip through undetected. Though the recent increase makes clear that the flow of migrants has resumed, the numbers have not approached the crisis levels of 2014, when they reached nearly 70,000 in a single month, many of them children traveling alone. Homeland Security officials noted that the 2017 apprehensions still represented a 40 percent decrease from the year before.

“The final border apprehension numbers of 2017, specifically at the southern border, undeniably prove the effectiveness of President Trump’s commitment to securing our borders,’’ Tyler Houlton, a spokesman for the agency, said in a statement. He also called on Congress to close what he said were “loopholes’’ that incentivized illegal immigration and were being exploited by migrants. By that, he seemed to reference the asylum system, as well as protections for children who cross the border without adult supervision.

Tens of thousands of people apply for asylum annually. The vast majority are denied, and cases can drag on for years, during which time many applicants are released from custody and establish ties to the United States, eventually deciding to stay illegally. Their numbers have contributed to an ever-growing immigration court backlog, with more than 650,000 cases now pending, up from 520,000 in late 2016, according to the Transactional Records Access Clearinghouse, a research group based at Syracuse University.

Among those stopped at the border in December were 8,000 families and 4,000 so-called unaccompanied minors. Family detention centers are so full that many families are being let go, with the parents fitted with ankle monitors, the kind of “catch and release’’ practice that the administration has been trying to avoid all along.

“The administration is committed to using all legal tools at its disposal to secure our nation’s borders, and as a result we are continuing to review additional policy options,’’ Houlton said.