WASHINGTON, April 29, 2010 -- Surrounded by cheering supporters, Florida Governor Charlie Crist announced today at a press conference he was dropping out of the Florida Republican Senate primary race to run as an independent.

"My decision to run for the United States Senate as a candidate without party affiliation in many ways says more about our nation and our state, than it does about me," Crist announced.

"For me it's never been about doing what's easy," he said today, "it's about doing what is right for the people first."

"Unfortunately our our political system is broken," he said. "I haven't supported an idea because it's a Republican idea or it's a Democratic idea, I support ideas that I believe are good ideas for the people."

The primary is not until Aug. 24, but polls showed Crist badly trailing former Florida House Speaker Marco Rubio, a Tea Party favorite.

Republican Senate leaders immediately slammed his decision, demanding Crist return money they donated to his campaign.

"Elections are about trust and frankly, it is unclear whether Governor Crist deserves any," said a joint statement from the National Republican Senatorial Committee. "We plan to put our resources and support behind Marco Rubio."

Crist's pollsters, the Republican polling firm of Public Opinion Strategies, announced today that it is resigning from his campaign.

"Governor Crist's decision has been ceaselessly speculated on in recent weeks. Despite his difficulties in the Republican primary, we were loyally working for him as long as he was a Republican. With his announcement that he is not running as a Republican, we will no longer be involved," said Glen Bolger, a partner in the firm who worked with the Crist campaign.

Many question whether Crist's switch is a warning sign for moderate Republicans across the country running for reelection this year.

But Rubio told ABC News in an exclusive interview today that he thought Crist's move had more to do with political convenience than ideology.

"In fact this has nothing to do with ideas or principles or ideology, it's about quite frankly political convenience. It's about someone who wants to continue his career in politics and doesn't believe he can do that this year within the Republican party," Rubio said.

Watch Terry Moran's day-in-the-life profile of Rubio tonight on ABC's "Nightline," at 11:35 pm ET, or go to www.abcnews.com/nightline.

The move sets up a tight three-way race between Crist, Rubio, and likely Democratic nominee Rep. Kendrick Meeks.

Crist previewed his move a week ago, when he told reporters he was listening to advice to make the switch.

"I think I'll take the advice of people in Florida instead of the advice of people in Washington," Crist told reporters last week. "They try to tell us a lot, and I don't think we need to listen. ... Things change."

Crist was once a rising star of the GOP -- much as his challenger Rubio is now. The Republican Party in turn made him one of the most powerful political figures in Florida, but he's since lost that support.

Many say the cause of the governor's slipping Republican support was Crist's embrace of President Obama -- literally.

In February 2009, the president visited Florida to promote the economic stimulus program, and invited Crist -- who supported it -- to appear onstage. After Crist finished his remarks, he and the president exchanged a quick embrace that Republican critics quickly seized upon.

More damaging than the embrace itself was Crist's support of the president's stimulus plan, blasted by many Republicans.

Republicans in Washington have been bracing for Crist to leave the GOP. They tried -- apparently in vain -- to persuade him to remain with the party.

But some Republicans say as Novembers mid-term elections draw closer, candidates are likely to move toward the party's core principles, and those like Crist are sure to be left out.

"I think that this has less to do with Crist being a Republican and feeling he has to take this set of Republican principles," Republican strategist Kevin Madden told "Good Morning America's" George Stephanopoulos. "Instead this has more to do with Crist and his political expediency. He cares more about his career than he does about his political party."

A Florida Republican source, who claimed not to have been notified personally of Crist's plans, told ABC News that the internal polling Crist got back this week showed that the only possible path for him to win the Senate seat was to run as an independent.

Democrats hope a split of the conservative vote will help their man, Rep. Kendrick Meek.

"Some people feel running against two Republicans is better than running against one," said Meek.

An April 13th Quinnipiac public opinion poll in Florida asked people how they would vote in a three-way race with Crist as an independent. The poll showed a tight contest: Crist with 32 percent, Rubio with 30, and Meek with 24.

ABC News' Teddy Davis, David Chalian and Gary Langer contributed to this report.