As U.S. President Donald Trump intensifies his campaign against diversity programs, appointments of women and racial minorities to S&P 500 boards have dropped to their lowest level in more than a decade, threatening to unwind years of gains in corporate boardroom diversity.

The shift is evident in new research by recruiting firms that study leadership diversity and interviews with more than a dozen boardroom recruiters, investors and human resource analysts.

It follows a series of Trump administration actions targeting diversity, equity and inclusion (DEI) initiatives. Across corporate America, major investors who once pressed companies to diversify their boards have retreated, while legal challenges have upended DEI policies in recent years.