For much of the 20th century, political polarization within the United States House of Representatives tended to decrease over the course of a two-year term. But starting in the mid-1980s, that trend reversed, and in recent decades, polarization has been more likely to grow.
source https://www.lifetechnology.com/blogs/life-technology-news-blog/forces-behind-growing-political-polarization-in-congress-revealed-in-new-model