It doesn't goto nearly zero. TSMC has a large fab in Arizona and they are continuing to expand it. They also have a fab in Washington, and in Japan. [1]

[1]https://www.tsmc.com/english/aboutTSMC/TSMC_Fabs

The fab in Washington is very old (notice it's still equipped for 8 inch wafers) and so pretty irrelevant to Nvidia's business.

I'm not quite sure what process they run there but I believe it was an acquisition 10+ years ago, not built from the ground up by them.

Edit: their Japan fab is also a mature node so not very relevant here. And their Arizona fab is a very very small portion of their volume and with far worse margin.