Without immigration, the U.S. population will shrink starting in 2033 in part “because fertility rates are projected to remain too low for a generation to replace itself,” the Congressional Budget Office said.
The reduced projections from last year were the results of a decline in projected fertility rates over 30 years from 1.70 births per woman to 1.60 births per woman and less immigration because of an executive order last June that temporarily suspends asylum processing at the border when U.S. officials deem they are overwhelmed, the budget office said. Replacement happens at a rate of 2.1 births per woman.
Without any migrants in either direction you would still need to account for deaths before having children, infertility and similar effects, that is why the figure given for a stable population is usually 2.1 and not 2.001 or something similar like your 2001 figure.
yeah, I was saying the 2001 as like, a simplification, in a vacuum, absolute minimum needed. Just something to illustrate the issue, reality is usually different, more complicated