In Texas, Tennessee and other Republican-led states, legislators have passed scores of laws restricting the lives of transgender people. They have made it illegal for transgender minors to get certain medical treatments and have threatened to have their parents investigated.

It made Jesse Thorn, the father of two transgender daughters, angry and sad. But he was never afraid. His family lives in California.

“For months and months and months,” Mr. Thorn said, “when someone would say, ‘I’m so sorry this is happening to you,’ I would say, ‘Thank you for loving my family, but it’s not happening to me. My kids are fine. Let’s see what we can do to take care of other kids.’”

All of that has changed. The clinic where Mr. Thorn’s family has received treatment for years is closing.

It is one of two prominent medical centers in California that are sharply cutting back gender-related treatments for transgender youths under pressure from the Trump administration. The moves have sent shock waves through L.G.B.T.Q. communities in a Democratic-controlled state long known for its trans-friendly politics and culture.

Children’s Hospital Los Angeles on Tuesday shuttered its Center for Transyouth Health and Development, one of the nation’s oldest and largest clinics for transgender and gender nonconforming young people and the clinic where Mr. Thorn’s family had been patients. Stanford Medicine in the San Francisco Bay Area has paused surgical procedures, including new puberty blocker implants, for those under the age of 19. Together, the facilities served thousands of patients.

Other hospitals in cities and states led by Democrats have also moved recently to curtail transgender services to minors.

UChicago Medicine announced last week that it was ending all pediatric transition care, days after another Chicago-area system, Rush University System for Health, said it was pausing hormonal treatment to new patients under the age of 18. In Washington, D.C., Children’s National Hospital announced it was discontinuing the prescription of transition medications starting Aug. 30. And the University of Pittsburgh Medical Center said its clinicians would no longer provide puberty blockers and hormone therapy for those under the age of 19.

The Trump administration has succeeded in thwarting transgender treatment for minors in some of the most heavily Democratic places in the country by adopting an aggressive approach, threatening to eliminate federal funding at individual hospitals and sending providers subpoenas seeking confidential patient information.

In California, transgender minors and their supporters had long viewed the state as a haven for transgender rights. More than two dozen states have passed laws prohibiting gender-transition treatments for minors since 2021, but California leaders went the opposite direction, passing legislation aimed at protecting families seeking transition care in the state. And a Supreme Court decision in June reinforced the idea that states would control whether young people had access to treatments for gender transition.

Now, families of transgender minors in California are searching for alternate treatment facilities. Many say they are angry with the Trump administration, but also with Gavin Newsom, the Democratic governor. Families and trans advocates say they feel betrayed by Mr. Newsom, as well as by health care administrators, who they say have capitulated to an administration intent on turning transgender children into scapegoats.

Gender treatments for minors, which can include puberty-blocking drugs, hormones and, in rarer cases, surgeries, are at the center of intense debate around the world. In the United States, clinicians and families say that the treatments can be lifesaving for transgender adolescents, while some critics on the right and left have argued for banning them, saying that minors are not equipped to make potentially irreversible decisions about their medical care. The American Academy of Pediatrics continues to endorse the treatments, but has said it is conducting a review of the evidence.

The number of minors who medically transition is small, but demand for the treatments has increased in recent years, and countries have responded differently. Health agencies in England, Sweden and Finland have limited the treatments, citing uncertain evidence of the benefits and risks, while Germany has endorsed them, citing a lack of effective alternatives. None of these governments have banned the care.

In interviews, nearly a dozen people affected by the closures in California, including transgender patients, parents and staff members from Children’s Hospital Los Angeles, described a small, tight-knit community that is now scrambling to continue essential medical care, much of which has been carefully planned in consultation with doctors over years. Many of those interviewed spoke on the condition of anonymity because they said they feared retaliation, including the possibility of prosecution by the federal government or loss of their Medi-Cal coverage, the state’s federally funded health insurance.

Some families said they were looking for new doctors and institutions in California, and making backup appointments in case those providers also abruptly cut off services. Some said they were even considering moving to other countries, in case treatment became impossible to find. Mr. Thorn and his wife were considering a move to Mexico City, while other parents were looking into Ireland.

A 16-year-old transgender girl whose long-awaited appointment to get a puberty blocker implant at Stanford was canceled abruptly said she used to be primarily concerned about the growing acceptance of slurs and bullying directed at trans people.

Now, she said, she is more worried about the prospect of losing her medical treatment and going through male puberty, a possibility that she said would further alienate her from her own body. The girl, whose mother allowed her to speak to a reporter on the condition of anonymity out of fear for her safety, still has access to puberty-blocking injections at Stanford, which last for several months. But she said an implant, which is placed under the skin and releases puberty-blocking drugs for more than a year, would have provided more stability.

Her body, she said, feels like “a ticking time bomb.”

Trump administration officials have called gender treatment for minors mutilation. In May, the Department of Health and Human Services published a report that seemed to call into question the notion that some people have a gender identity that does not align with their sex at birth.

“Parents who are desperate to help their confused, frustrated children have understandably turned to medical professionals for help,” Attorney General Pam Bondi wrote in a memo that called for gender treatments for minors to be investigated and prosecuted as genital mutilation. “Unfortunately, those parents have been betrayed by politically captured profiteers at every step.”

In January, Mr. Trump signed an executive order directing federal agencies to withhold grant funding for research and education from medical providers that offer gender-transition treatments to people under the age of 19. That directive was temporarily blocked across the country by a federal judge in Baltimore, who found that the administration had most likely exceeded its authority and violated the equal protection rights of transgender plaintiffs. In a separate case, a federal judge in Seattle blocked the government’s health agencies from carrying out the order in Washington, Oregon, Minnesota and Colorado. The government has appealed both cases, but it has also looked for other ways to pressure hospitals to stop providing such services.

In June, the clinic in Los Angeles, which had treated thousands of patients over more than three decades, said in a letter to staff that it would soon be shuttered. Protests were held outside the hospital. In the weeks leading up to the closure on Tuesday, staff members and patients said the office had been stripped of Pride flags, its walls left bare.

“The closure at Children’s Hospital hit like an earthquake here,” said Arne Johnson, the parent of a transgender 13-year-old and a member of Rainbow Families Action, a transgender rights advocacy group in the Bay Area. He added that the willingness of prestigious institutions like Children’s Hospital Los Angeles and Stanford to cut services under pressure from the federal government did not bode well for other contentious areas of health care, including vaccines.

“This is not going to be the last group of parents who are watching their kids’ care being taken away,” he said.

Marlen Bugarin, a spokeswoman for Children’s Hospital Los Angeles, declined to comment.

Dr. Johanna Olson-Kennedy, the clinic’s medical director, has long been an outspoken advocate for pediatric transition treatment and has served as an expert witness in many legal challenges to state bans on the care. Her approach, which prioritizes early intervention, has inspired deep loyalty from many of her patients, but it has also attracted fierce condemnation from conservative groups and scrutiny from other clinicians. Dr. Olson-Kennedy did not immediately respond to a request for comment.

In a letter to staff members, Children’s Hospital Los Angeles administrators wrote that they did not want to close the clinic, but that they were facing legal and financial uncertainty from the presidential executive order, court rulings and new rules by federal agencies. More than 65 percent of the hospital’s annual $2 billion in funding comes from federal sources, the most of any pediatric hospital in the state, the letter said. The Trump administration’s threats to that funding, the letter said, created “an immediate and unsustainable strain on our fiscal resiliency.”

Adding to the pressure on medical institutions, the Justice Department issued subpoenas this month for confidential patient information from more than 20 providers of transition treatment for minors.

Medical centers in California and elsewhere find themselves in a bind. They have angered and disappointed transgender patients, their families and their advocates, drawn the hostile attention of federal officials and opened themselves up to potential litigation.

Mr. Newsom’s office called the suggestion that he hasn’t done enough to protect transgender Californians “insulting.”

“Maybe folks should look to Washington,” Izzy Gardon, a spokesman for the governor, said in a statement. “The governor’s record supporting the trans community is unmatched.”

Mr. Newsom has been a supporter of L.G.B.T.Q. causes and was one of the first elected officials in the United States to officiate same-sex weddings. In 2022, he signed the law that aimed to shield trans patients and their families from prosecution by out-of-state authorities.

“We believe that no one should be prosecuted or persecuted for getting the care they need — including gender-affirming care,” he said at the time in a statement. “We must fight for our youth and their parents.” But in recent months, Mr. Newsom — who has been viewed as a possible presidential hopeful — has angered L.G.B.T.Q. Californians by seeming to shift to the right, most notably by saying on a podcast episode with a conservative activist that the participation of transgender athletes in women’s sports is “deeply unfair.”

His remarks illustrate changes within the Democratic Party over the issue. Polls show support for some restrictions on transgender rights growing among Democrats, including restrictions on medical care for transitioning minors.

One 21-year-old transgender woman who was a patient at the Children’s Hospital Los Angeles clinic said the effect of the closure would be far-reaching.

The young woman, who asked to be identified only by her first name, Langston, out of concern for her safety, said she realized she was trans while she was in college. She had been suffering from depression, which she said “stemmed from the fact that I was not who I wanted to be.” Her parents were surprised and worried, but encouraging, when she came out to them. Langston’s visits to Children’s Hospital Los Angeles, she said, helped her and her family find their way.

“My mom was coming with me to appointments and sometimes she’d be in the room, and they know how to handle her as a parent, which is a skill,” Langston said. “That’s one of the things I’m going to mourn.” She added: “There’s going to be a lot of people who are directionless.”

Azeen Ghorayshi, Amy Harmon and Joseph Goldstein contributed reporting.