ST. PETERSBURG — Over two decades in politics, Charlie Crist has developed a reputation as one of the most charming politicians in modern Florida history. But Monday, as the former Republican governor kicked off his Democratic campaign for governor, he left no doubt his challenge of Rick Scott will be anything but gentle.

"Governing for the people has been replaced with cronyism and government on the fringes," Crist told nearly 200 people gathered to cheer him along St. Petersburg's downtown waterfront. "The voice of the people has been silenced by the financial bullies and the special interests."

Crist's rally occurred exactly one year before Florida voters decide whether to give Scott a second term and marked the start of what is likely to be the most negative and lavishly funded campaign Florida has ever seen.

As Crist spoke, a plane flew overhead carrying a banner directing people to a website mocking the former governor who in three years has campaigned as a Republican, an independent and now as a Democrat.

Gov. Scott's political committee "Let's Get to Work" also began airing negative TV ads casting Crist as a craven opportunist, the start of what Scott has said will be a $100 million re-election campaign. Other Republican officials lined up to attack their former party leader who walked away from the governor's mansion in 2010 to run unsuccessfully for U.S. Senate.

"If Charlie Crist wants to be governor so bad again, why did he leave Florida in our time of great need, when we had over an 11 percent unemployment rate with 832,000 people out of work?" said Florida House Speaker Will Weatherford, R-Wesley Chapel. "Florida really needed a leader then, but he turned his back on our state. If we couldn't count on him then, how can we count on him now?"

Crist, 57, took aim at Scott.

"Gov. Scott has led like this: Embrace the ideological fringes, take care of his friends, bully his opponents, hide from the public and the press and run from tough issues. Shouldn't really come as a surprise, though. Think about it: He hid from federal investigators as a businessman and his company had to pay the largest fine at the time for fraud in the history of America," Crist said, referring to Scott's former career leading the Columbia/HCA hospital chain and its record $1.7 billion fine for alleged Medicare fraud.

Scott campaigned as an outsider determined to shake up Tallahassee, Crist said, but "overnight, he went from taking on Tallahassee to becoming the example of what's wrong with the place. The seat that you occupied — that the people occupied — at the table was replaced by a revolving door of special interests, each anteing up hundreds of thousands of dollars to the governor's re-election fund to ensure their voice was heard and not yours."

Public polls consistently show Crist leading Gov. Scott, by double digits in some cases, but Republican backers note that those polls do not reflect what tens of millions of dollars in negative ads can do to Crist's image.

Critics will paint Crist as a self-serving flip-flopper with no core beliefs and as a weak governor who oversaw soaring unemployment while the Florida economy improved after Scott took office.

"Charlie Crist was a failure as governor and is a pure political opportunist who is out for himself. Under Crist, Florida lost over 800,000 jobs, saw their unemployment rate surge from 3.5 percent to 11.1 percent, and experienced a budgetary crisis that left the state sinking faster and faster," said Louisiana Gov. Bobby Jindal, head of the Republican Governors Association. "And when the going got tough, Charlie dropped his rifle, abandoned his post and ran away from the people of Florida. If you like losing jobs and are looking for a politician who blows with the wind, Charlie Crist is your guy."

Democratic former state Sen. Nan Rich, 71, of Broward County has been running for governor for more than a year, but she has raised little money. On Monday, Rich challenged Crist to 10 debates.

"Charlie is a Democrat now — but he's changed more than his party registration — he's changed his stance on many major issues and voters I've met with wonder how committed he is to his newfound positions," Rich said.

Crist has one particularly influential Democratic fan: President Barack Obama. The president asked Crist — the only Republican governor to support the $787 billion federal stimulus bill in 2009 — to speak at the Democratic National Convention last year, and Crist campaigned throughout Florida for the president's re-election.

Now, Crist is turning to Obama's political team to help run his first campaign as a Democrat. Crist has hired media consultant Jim Margolis and pollster John Anzalone as well as Tallahassee-based strategist Steve Schale, who ran Obama's 2008 Florida campaign.

Obama's team has also helped introduce Crist to prominent Democratic fundraisers across the country.

Following the lead of Gov. Scott, who created a special committee that can accept unlimited campaign contributions, Crist has created the "Charlie Crist for Florida" committee. Its chairman is Bob Poe of Orlando, a top Obama fundraiser and former chairman of the Florida Democratic Party.

The broad platform Crist offered Monday sounded similar to his platform as a moderate Republican governor: more money for public schools, tax cuts to help small businesses and middle-class Floridians, investments in clean energy and infrastructure including roads, ports, and high-speed rail. He is sticking with his old slogan: "The People's Governor."

Repeating another theme from his term as governor, he touted the importance of bipartisanship: "When the people give you the honor of being their governor, you aren't the governor of any one party, you are the governor of all Floridians," said Crist, who was joined on stage by his wife, Carole, U.S. Rep. Kathy Castor, D-Tampa, former Attorney General Bob Butterworth, former state Sen. Dan Gelber, D-Miami Beach, St. Petersburg mayoral candidate Rick Kriseman, and longtime friend Watson Haynes, president of the Pinellas County Urban League.

"No matter what they say, it is not a sin to reach across the aisle," Crist said. "It is your obligation to work together."

Times staff writer Julie Kliegman contributed to this report.