NEW YORK (AP) — President Joe Biden is proposing to nearly double the tax rate that the highest-earning Americans pay on profits made from stocks and other investments. The proposal would force millionaires to pay similar tax rates on their investment gains as upper-middle class households pay on their salaries. And it has already caused some turbulence in the stock market. Proponents say the higher tax rate would help pay for needed improvements and create a more fair system. Opponents say it could lead to less investment and discourage entrepreneurship. Either way, past increases in the tax rate have led to only short-term stumbles for stocks.