The American Enterprise Institute in 2015:

“[Nicolas] Eberstadt [of the American Enterprise Institute] sees US demographic trends as mostly positive. The US, the world’s third-most-populous country (321.4 million people) and largest economy (GDP of $18.1 trillion), is projected to have modest population and working-age population growth over the next 20 years. And its population will age more slowly than in other OECD countries. The US still has a positive replacement-level fertility rate, augmented by continued immigration, including an influx of highly educated immigrants at a rate above the OECD average, he said. Eberstadt sees immigration in the US and Canada as a “fantastically positive experience” for those countries.” (Quoted here.)

The American Enterprise Institute in July 2025:

Report: “Immigration Policy and Its Macroeconomic Effects in the Second Trump Administration”

This AEI report projects that U.S. net migration in 2025 will fall to between −525,000 and 115,000 and reduce GDP growth by 0.3–0.4 percentage points. Its model estimated that if low immigration persists, GDP in 2034 would be roughly 1–2 percent smaller than under normal migration levels. That is to say, the GDP in 2034 would be about 41 trillion with pre Trump prevailing immigration and about 40 trillion without.  Thus its model expects a modest adverse impact.