Two months ago, Roseanne Barr was a star again.

Her sitcom “Roseanne” returned in March after a two-decade absence to enormous ratings on ABC. Network executives were celebrating their strategy of appealing to wider swaths of the country after Donald Trump’s surprising election win and the president himself called Barr to congratulate her on the show’s large audience.

But on Tuesday, that all came crashing down. ABC abruptly canceled “Roseanne” hours after Barr, the show’s star and co-creator, posted a racist tweet about Valerie Jarrett, an African-American woman who was a senior adviser to Barack Obama throughout his presidency and considered one of his most influential aides. Barr wrote if the “muslim brotherhood & planet of the apes had a baby=vj.”

Barr later apologized, but it was too late. In announcing the show’s cancellation, ABC Entertainment President Channing Dungey said in a statement that “Roseanne’s Twitter statement is abhorrent, repugnant and inconsistent with our values.”

The show had ended its successful comeback season last week and was expected to return in September for a 13-episode run. Robert Iger, chief executive of the Walt Disney Co., ABC’s corporate parent, shared Dungey’s statement on his own Twitter account, adding: “There was only one thing to do here, and that was the right thing.”

The sudden cancellation of a hit show — it had the highest ratings of a new TV series in years — because of off-screen controversy was almost without precedent.

The move was decided by top Disney and ABC executives, including Dungey, who was appointed to her role in February 2016, becoming the first black entertainment president of a major broadcast television network. She had the backing of Ben Sherwood, the head of ABC’s television group, and Iger, who was involved in the process starting very early Tuesday, according to two Disney insiders who spoke on the condition of anonymity to describe company matters.

There was more at stake than a hit show. Disney has been widely praised in recent years as a leader in efforts to combat racial stereotypes through its movies and TV series, whether on “Doc McStuffins,” a Disney Channel cartoon about an African-American girl who wants to be a doctor; “How to Get Away With Murder,” a vehicle for Viola Davis that led her to become the first black woman to win a lead-actress Emmy; and “Black Panther,” which smashed an entertainment-industry belief that movies rooted in black culture and with predominantly black casts could not become global blockbusters.

If Disney did not act forcefully with regard to “Roseanne,” much of that work might have been rendered moot.

It did not take long for ABC to move on. A repeat episode scheduled for Tuesday night was promptly replaced with a rerun of “The Middle.” The network also began the process of taking each episode of “Roseanne” off its website.