You got me thinking: both
@panpiotr and myself might have missed the GDP per capita.
Say the Union State has 200,000,000 inhabitants in 2028. The $27.576.445 million GDP, gives us a per capita number of $ 137,882.22. That is a lot. The most recent numbers I could find with a quick Google were for 2022 & 2024. If we assume the Union State has 190,000,000 inhabitants, we'd be at $ 109,674.23 per capita, which is between Nr 5 Quatar and Nr 6 UAE. The USA is 8th, at 76,399. For 2024 the USA is at p6 at $ 85,370, while we'd be at $ 112,076.19. That's P2 between Luxembourg and Ireland (with a Union State population of 193,000,000).
So we need about 50,000,000 people to have a GDP per capita to be close to the USA. If we compare ourselves with say Norway, which is a 1st world country with lots of natural resources, we need 30,000,000. If we compare ourselves to Germany, we need a staggering 205,000,000 extra people.
TLDR; we need the Stans (appr. 72 million). Preferably with Ukraine (appr. 38).
Edit: if we add the Stans in 2023 (1,205 GDP, 72,000,000) we get $ 78,407,45, much more realistic.
Edit2: the other way around works too, but then we'd be richer per capita as the US. If we add Ukraines adjusted 2024 GDP and pop we come to $ 102,272 in 2024. Pretty high.