We're already seeing the effects. Many people don't feel secure enough in their finances, or confident enough in the future they'd be bringing children into to have kids. As far as I can tell things will only get worse long before they even have a chance to get better.
I'm in that group. The thing is China already crossed that rubicon 20+ years ago. So the US only really needs to outlast China in this regard. It will create problems of its own and pro America people like Peter Zeihan argue that large generations create more large generations. Boomers -> Millenials -> Gen Alpha. I dont fully buy this though.
Their population pyramid looks good though compared to China:
https://www.populationpyramid.net/united-states-of-america/2...
If the 1930s are any example, war will follow, then a baby boom after the war