The growth in the working-age population over the next two decades is dependant on the arrival of future immigrants, according to a Pew Research Center study.
The number of working-age immigrants is projected to increase from 33.9 million in 2015 to 38.5 million by 2035, the study shows, with new immigrant arrivals accounting for all of that gain, based on current rates of immigration, both lawful and undocumented.
The number of current immigrants of working age is projected to decline as some retire and others are projected to leave the country or die. Without new arrivals, the total projected U.S. working-age population would fall from 173.2 million to 165.6 million by 2035, Pew found.
The number of illegal immigrants crossing into the U.S. from Mexico went down by 40 percent from January to February, according to the U.S. government. Homeland Security chief John Kelly said the "change in trends" was a result of Donald Trump's tough policies.
The president has signed an executive order to expand the existing border "wall" and issued new priorities for deportations.
“In recent decades, immigration to the U.S. has become an increasing source of growth for the working-age population,” Pew states. A growing labor force is key for economic growth as well as the ability to pay social benefits for retiring workers.
Kelly said on Wednesday that the number of "inadmissible persons" crossing the U.S.-Mexico border had dropped this year from 31,578 to 18,762 in January to February - a period when the number of arrests of illegal immigrants normally increases.
"Since the administration's implementation of executive orders to enforce immigration laws, apprehensions and inadmissible activity is trending toward the lowest monthly total in at least the last five years," he said.
Trump has made immigration policy a key part of his "Make America Great Again" mantra, blaming undocumented immigrants for crime rates and taking away jobs from U.S. citizens.
"The decrease in working-age adults born in the U.S. whose parents also were born in the U.S. largely reflects the aging of the Baby Boom generation born from 1946 to 1964," according to Pew. The youngest Boomers turn 65 by 2030.