TALLAHASSEE — To friends and political allies, Mel Sembler is a real estate developer with integrity.

A former ambassador and shopping center magnate, he remains a giant of Tampa Bay politics. His influence stretches from his $3.4 million St. Petersburg penthouse to a network of insiders cultivated from the last three Republican presidencies.

To others, Sembler is known as the founder of Straight Inc., a controversial drug treatment program that operated from 1976 to 1993. He and his wife, Betty, started the residential program to help troubled teens. Yet after opening in about a dozen states, it was shut down amid allegations of abuse and excessive force. Some subjected to the program's get-tough therapy now say years were stolen from their lives.

Now 86, Sembler is using his clout as one of the most powerful figures in Florida politics and the anti-drug movement to defeat a constitutional amendment aimed at expanding medical marijuana in Florida. If passed by 60 percent of voters, Amendment 2 would let doctors recommend marijuana to patients with conditions like cancer, epilepsy and HIV/AIDS.

Sembler has so far donated $1 million to defeat the constitutional amendment. A former national Republican finance chairman, he's tapped his cadre of wealthy donors, too. He says he'll raise $10 million for Drug Free Florida, the political committee opposing the ballot measure.

But as Sembler leads the fight, the controversy surrounding Straight continues to haunt his anti-drug legacy.

"This was the first and only controversy I've ever known having to do with Mel Sembler, and it's regrettable," said Pat Neal, a Sarasota home builder and former state senator, who gave $10,000 to the Drug Free Florida effort. "He only wanted to do the right thing."

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For a man with such an outsized role in shaping a public policy like medical marijuana, Sembler doesn't reveal much.

He declined a Times/Herald interview and does not publicly talk about why he got involved in the anti-drug movement.

News reports from 20 years ago say his interest started in the 1970s, when he and Betty, parents of three sons, learned that one them was smoking marijuana.

The couple started Straight, which was modeled after a previous anti-drug program called The Seed. Its ambitious goal: end teenage drug use.

"I knew young people who really got straightened out at Straight," Neal said. "It was very controversial, but it was also very effective."

The idea caught fire, gaining traction in the upper reaches of President Ronald Reagan's administration.

Sembler was one of the people who suggested that first lady Nancy Reagan lead the anti-drug movement, said Maia Szalavitz, author of a 2006 book on the troubled-teen industry, Help at Any Cost.

The White House entrée led to the Bush family. George H.W. Bush later named Sembler ambassador to Australia and Nauru.

"He is someone that local elected officials go to for advice, but he is approachable by heads of state as well," said state Sen. Jeff Brandes, R-St. Petersburg, the first state senator to endorse Amendment 2. "He's a legendary figure."

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Marcus Chatfield never met Mel Sembler.

But he was forever changed by him.

As a teen, Chatfield had shoplifted, run away from home and smoked pot a few times. He was never addicted to drugs, he says.

But he told people he was addicted in hopes of avoiding juvenile detention. Instead, Chatfield was sent to Straight's Springfield, Va., facility, where he spent more than a year, most of it on a judge's order.

He spent hours of every day in what Straight called "raps" — group meetings where other teens were expected and sometimes bullied into confessing harrowing stories about drugs and alcohol use. Chatfield said they were encouraged to yell at and shame one other.

Many participants had only a few stories to share, but they were under constant pressure, Chatfield said. So he started to lie.

"And after some time, I started to believe it," he said.

He said some of the worst abuses were at the hands of other students. After Chatfield had been in the program for several months, he was allowed to start going to school and was placed in charge of other children. He said he followed orders and deprived children of sleep. Sometimes, he said, he and others were told to pin someone on the ground for an entire rap session for acting out.

"That stuff haunts me," he said. "That stuff will always haunt me."

Now 47, Chatfield lives in Micanopy, where he's a family, youth and community sciences graduate student at the University of Florida. He wants to conduct research into the lasting effects of Straight-style treatment programs.

Straight ultimately came under fire for holding people against their will. Court rulings led to policy changes, and ultimately Straight shut down.

Friends give little credence to claims of abuse and say the Semblers were not aware.

"I know Mel and Betty. I know where there heart was," said Susan Latvala, a former Pinellas County commissioner. "I think it's inappropriate to keep dragging that up."

A 1993 Florida Inspector General audit suggested Sembler was aware. The report said that despite "a propensity for abuse or excessive force," Straight kept getting licensed.

"It appears that pressure may have been generated by Ambassador Sembler and other state senators," the report stated.

A year later, Straight had dissolved.

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To Mel Sembler, fighting medical marijuana is a continuation of his and Betty's life's work.

"We're trying to save lives and people's brains," he told the Times/Herald in April. "It's not a medicine."

In 1995, Straight's name was legally changed to Drug Free America Foundation, state documents show. The organization no longer provides treatment.

Its work continues in financing campaigns opposing marijuana, both recreational and medical use, which many opponents say could lead to full legalization. Latvala and Neal have served on its board of directors.

With marijuana on ballots across the country, the group is considering more public awareness campaigns, Latvala said.

Yet given Straight's history, Szalavitz was dismayed that the Semblers were shaping public drug policy. After spending five years researching adolescent centers for her book, she confirmed numerous allegations of abuse at Straight.

"They should have no sway over drug policy in any way," she said.

Times senior researcher John Martin contributed to this report. Contact Michael Auslen at mauslen@tampabay.com. Follow @MichaelAuslen.