[pertymcpert]

In the modern world, 1.8 is very solid. Easily can make up for that with immigration.

[bombcar]

At some point you run out of places for people to immigrate from unless you just empty entire countries.

[satvikpendem]

Until the US ceases to be a desirable destination for many immigrants, which could take quite a while.

[Dylan16807]

That's not something to worry about until the global population stops (rapidly) growing.