Investing another $400 billion in the US sounds like a bigger commitment than buying Intel.

I am not even sure what TSMC would do with 49% of Intel. Upgrade their Intel's existing fabs using TSMC tech? I can't imagine TSMC getting into developing semiconductors (e.g. x86 CPUs), doesn't seem to fit their strategy and Intel only strong position is x86 CPUs for laptops.

A mere decrease of tariffs from 20% to 15% doesn't seem all that enticing (without security guarantees for Taiwan), one would think TSMC could easily make their customers eat the 5% extra tariff cost, it's not like they have much of an option.