There's no doubt about it. Economic activity correlates with population. There are a number of things the US needs to do to ensure our population does not collapse. Ending insane sex education programs in schools that are basically grooming young children for abuse would be one. Ending the vaccine program (HPV vaccine in particular has been linked to severe disability and causes "premature ovarian failure" in girls) would be another. Anyway, the stats are pretty bad.
https://www.zerohedge.com/geopolitical/global-births-population-potential-mothers-down-down-down
https://www.reuters.com/article/us-health-maternity-costs/even-for-insured-women-having-a-baby-in-the-u-s-is-costly-idUSKBN1Z7300
Women in the US have worse pregnancy outcomes and when they do have children those babies suffer relatively high infant mortality. I believe that in the developed world the US has the highest rate of death on the first day of life (Hep B vaccine, plus "Vitamin K" injection are possible culprits).
Across the globe, Africa is the only continent which is not (apparently) suffering from demographic decline.
We need to do something-yesterday. I think Hungary is worth looking at. They gave deliberate tax breaks to native Hungarians who marry and have children. They acknowledge that Hungary has a religious Christian heritage. They eliminated stupid college degrees in subjects like "gender studies" etc. They do not support mass immigration. Last I knew the native population of Hungary was moving in a positive direction.