Updated: 12:53 p.m.Sen. Mel Martinez (R-Fla.), who had already announced he was retiring at the end of 2010, has decided to call it quits early and will resign his office in the near future.Martinez, whose decision was first reported by CNN, is set to make an official announcement at a 3 p.m. news conference at the Orlando International Airport. He is expected to remain in office until Florida Gov. Charlie Crist (R) lines up a successor.Crist, who is running to replace Martinez, is seen as likely to appoint a placeholder to fill the vacancy, instead of appointing himself — a move that could create a political backlash and damage his chances of winning in 2010.Immediate speculation among party insiders about whom Crist might appoint as a placeholder centered on former Gov. Bob Martinez (R), Florida GOP Chairman Jim Greer and former Lt. Gov. Toni Jennings. In a statement released by his office, Sen. Martinez said that after 12 years of public service, he has decided it is time to return to Florida to be with his family.“My priorities have always been my faith, my family and my country and at this stage in my life, and after nearly twelve years of public service in Florida and Washington, it’s time I return to Florida and my family. So today I am announcing my decision to step down from public office, effective on a successor taking office to fill out the remainder of my term,— Sen. Martinez said.Sen. Martinez informed GOP leadership of his decision early Friday, Republican sources said.Crist has already won the backing of the party’s establishment, despite the fact that conservative former state Speaker Marco Rubio (R) is also running in the primary.In a statement, Rubio took a clear shot at Crist — whom conservatives have attacked for working with the Obama administration on climate change and the economic stimulus plan. Rubio called on Crist to appoint an interim Senator who opposes President Barack Obama’s policies.“As Governor Crist considers who he will appoint as Florida’s next U.S. senator, I urge him to take great care in his selection. Florida deserves an interim-senator who will go to Washington and serve as a true check on President Obama’s push for more wasteful government spending, government-run health care and cap-and-trade,— Rubio said. “The last thing Florida needs is a U.S. Senator that will stand with President Obama instead of challenging the wrong direction he is leading our country and offering constructive conservative solutions moving forward.—Bob Martinez, who is not related to the Senator, served one term as governor, from 1987 to 1991, and he was the first Hispanic to serve in that office. Before that, he was mayor of Tampa for six years. Crist is also from the Tampa Bay area, and sources said his relationship with Bob Martinez goes back many years.After leaving the governor’s mansion, Bob Martinez was appointed national drug czar by President George H. W. Bush, and he served in that position until January 1993.According to Florida GOP sources, Greer, like Bob Martinez, would act simply as a placeholder and is generally a noncontroversial figure in state politics. However, his close association with Crist could further anger the conservatives backing Rubio in the primary.Jennings served as lieutenant governor under Gov. Jeb Bush (R), and she might be viewed as the favored choice among conservatives. Sen. Martinez said in his statement that he has enjoyed his time in the Senate and that he has the utmost respect for his colleagues and the institutionHowever, his decision to leave office early is not a completely shocking development to Florida political insiders or national party strategists. There were rumors earlier this year that the Senator might be eyeing an early exit. It has been widely known that Sen. Martinez’s heart had always seemed to be set on running for governor. Heavy pressure from the White House, including top political strategist Karl Rove, is what ultimately persuaded Sen. Martinez to run for an open Senate seat in 2004.He wasted little time in announcing he would not seek another term in 2010. His retirement announcement came in November 2008, just days after the last elections.Meanwhile, Florida Democrats urged Crist not to play politics with the appointment. “U.S. Senate seats should not be political footballs,— Florida Democratic Party Chairwoman Karen Thurman said in a statement. “The last thing Florida needs are Republicans playing politics with a U.S. Senate seat while we face the largest economic crisis of our lifetimes and the Congress is tackling critical issues such as health insurance reform and global warming, so it is critical that Charlie Crist not play political games with the public’s trust.—The winner of the GOP primary is likely to face Rep. Kendrick Meek (D-Fla.) in the general election. Meek released a statement Friday praising Sen. Martinez. Republicans are currently favored to hold the seat in 2010.