Short-term capital gains are taxed as ordinary income, so an increase in short-term capital gains could push you into a higher marginal income tax bracket. The highest marginal income tax rate is 37%.
Long-term capital gains won’t affect your ordinary income tax rate, but increased long-term capital gains could push your long-term capital gains into a higher tax bracket. Most investors won’t exceed a 15% tax rate on their long-term capital gains.