Will the US top the 400 million population mark or no?
 

Do you think the US population will reach this milestone? Why or why not?

Barring a plague, major population reducing war or a drastic and long term decline of the western economic model I don't see how we cant?

We grow by about 2-3 million people a year, we are already closing in on 325 million.

We will hit 400 million in about 30-40 years, almost certainly.

Yes, the question is will we hit 1 billion some day.

International migration is huge and is required to keep the current economic system of consumption afloat. This could all change if we figure out how to maintain our lifestyle and entitlements with a stagnant system, but that has yet to be seen in a fiat currency system.

no, never

Collectively the Americas are well above this number:
Population 1,001,559,000 (2016 estimate)

I would say so..At the time of your Civil war, your population was just under Canada's current population of 35 million (31 million).So, from 1860(ish) to now your population increased ten fold. to add an extra 20-25% isn't out of reach..Even within the next 50 years.I know that birth rates aren't the same and there could be a lot of unforeseen variables hindering that curve, but it's definitely doable.

interesting to note, that Canada's population went from around 3.0 million to 35 million from 1860, or ten fold as well, but unless climate refugees become a real thing, I can't get my head around our population hitting your current population in 170 years. Another ten fold increase is a long shot.

Totally. I'd say by 2050.

Yeah, I'd say Canada will hit 50 million by 2050 while the US hits 400 million. Canada is growing % wise is growing faster than the US due to our larger per capita immigration numbers. The US used to be 10 times the size of Canada, now it's 9x and it's heading for 8x within the next 25 years.

I don't think either countries will get much bigger as the world's population peaks (thankfully) faster than originally estimated. The one thing COVID has done is permanently drop the birth rate.

How has Covid permanently dropped the birthrate?

I don't think that Covid has permanently reduced the birth rate (unless I am missing something).

That said, I do think that there is a population upper bound to the US economic system. It is probably around 400 million, and then maybe we could grow past that, but probably not without some fresh ideas.