President Trump had barely reacquainted himself with the Oval Office after his second inauguration when he began shredding the D.E.I. initiatives of the Biden administration, fulfilling a cause célèbre for conservatives that had helped power his political comeback.

On his second day back in power, Mr. Trump ordered that agency heads place those officials who had been responsible for overseeing diversity, equity and inclusion programs in the federal government on paid administrative leave and that their offices be shuttered.

Part of an executive action signed one day earlier, it was the first step in rolling back the D.E.I. policies that had been a hallmark of the administration of his Democratic predecessor, President Joseph R. Biden Jr.

This is how we got here:

What is D.E.I.?

D.E.I. stands for diversity, equity and inclusion. A page on the U.S. Department of Labor website, which was removed two days into the president’s new term, defined diversity as acknowledging all the ways that people differ. That can include race, sex, gender, age, sexual orientation, disability, socioeconomic status, religious beliefs and more.

“Organizations that respect diversity can come up with new ideas, solve problems, grow and run more efficiently,” the deleted entry on D.E.I. read on the agency’s website, which later read, “Page not found.”

It’s not new

While the three-letter abbreviation has become a hot topic in recent years, the principle has been around for decades in both the public and the private sectors. It developed as a result of the Civil Rights Act of 1964, which prohibited employment discrimination based on race, color, religion, sex or national origin.

Beyond the federal government, private companies, universities and nonprofit groups have put D.E.I. principles into practice.

D.E.I. policies expanded in the wake of George Floyd’s murder

The 2020 murder of George Floyd, an unarmed Black man who was killed by police officers in Minneapolis, ushered in a national reckoning over racial discrimination that brought sweeping changes to many powerful institutions and a renewed emphasis on D.E.I. initiatives, including actions by the Biden administration. (Mr. Biden unveiled a “racial equity agenda” on his first day in office in January 2021.)

A nonprofit made up of several of the largest U.S. companies asked its members to pledge to hire and promote Black workers based on skills instead of college degrees. An increasing number of brands such as Chick-fil-A, Bud Light and Target — through policies and advertising campaigns — adopted a mantra of being more inclusive.

For conservatives, three letters became a four-letter word

Having lost the presidency in 2020 to Democrats, who also controlled the House and Senate when Mr. Biden entered office, Republicans latched onto an emerging wedge issue, one that became a flashpoint in the 2024 election: D.E.I.

Those three letters became a staple of Mr. Trump’s campaign speeches, guaranteed to draw jeers from arenas full of his supporters in battleground states as he argued that the federal government and many companies had become “woke.” A 2023 ruling by the U.S. Supreme Court further emboldened conservatives by rejecting affirmative action at colleges and universities.

And when Mr. Biden was replaced as the Democratic presidential nominee in July by Vice President Kamala Harris, some of Mr. Trump’s allies in Congress disparagingly referred to her as a “D.E.I. hire.” In front of an audience of Black journalists in Chicago, Mr. Trump refused to disavow his supporters’ remarks and questioned Ms. Harris’s racial identity as a Black woman.

“She was Indian all the way, and then all of a sudden she made a turn and she became a Black person,” he said of Ms. Harris, whose mother was Indian American, whose father is Black and who has always embraced both her Black and South Asian identity.

What will Trump’s executive order change?

One day after Mr. Trump declared in his inaugural address that he would “end the government policy of trying to socially engineer race and gender into every aspect of public and private life,” his administration began purging D.E.I. staff members from federal agencies.

Those agencies were ordered to take down any language or advertisements about their D.E.I. initiatives and to withdraw any pending documents or directives that would undermine the new orders. The Trump administration threatened federal employees with “adverse consequences” if they failed to report on colleagues who had defied orders to eradicate D.E.I. efforts from their agencies.

Mr. Trump urged the private sector to take similar steps and directed agencies to investigate compliance by corporations and foundations. Companies working as contractors or subcontractors for the federal government could also find themselves bound by the new rules.

Some companies have already started to retreat from D.E.I.

After Mr. Trump’s victory in the 2024 election, several prominent companies started rolling back their D.E.I. initiatives. Among them were Walmart, McDonald’s, Amazon and Meta.

Still, some corporations have forged ahead with their racial and gender equity programs, including Costco and Microsoft.

Erica L. Green, Zolan Kanno-Youngs, Nell Gallogly, Steve Lohr, Mike Isaac, Sheera Frenkel, Kate Conger and Jordyn Holman contributed reporting.