> That's not how it works. The stockmarket is a comparative market where higher profitability compared to other companies is what affects stock price. This means tax increases to all companies don't drop stock prices.

The value of any stock (or bond or other financial asset) is its expected future cash flows discounted back to the present at a rate that reflects the risks associated with those cash flows. This is corporate finance 101. Higher taxes for US companies means lower cash flows, and lower values for those assets, unless the discount rate is lowered enough (e.g., lowering interest rates further, even going negative) to compensate. Companies with more US exposure will become less valuable, and money will flow to other assets, including bonds, foreign stocks, etc., to reflect the shift in value.