When Health Secretary Robert F. Kennedy Jr. threw his support behind Mr. Trump’s 2024 campaign for the White House, his corps of health conscious, mostly female, followers embraced the president, who pledged to address Americans’ concerns about “toxins in our environments and pesticides in our food.”

Some of the women, who call themselves the MAHA Moms after Mr. Kennedy’s Make America Healthy Again movement, abandoned the Democratic Party to vote for Mr. Trump.

But the executive order Mr. Trump issued Wednesday to increase domestic production of glyphosate — a widely used weedkiller and possible carcinogen that has been the target of thousands of lawsuits, including one brought by Mr. Kennedy — stunned and infuriated the activists. It now threatens to turn the brief MAHA-Trump marriage into a divorce.

“Women feel like they were lied to, that MAHA movement is a sham,” said Alex Clark, a health and wellness podcaster for the conservative group Turning Point U.S.A., which is closely allied with the president. “How am I supposed to rally these women to vote red in the midterms? How can we win their trust back? I am unsure if we can.”