FORT LAUDERDALE, Fla. – In a swift and stunning fall from political power, U.S. Rep. Mark Foley resigned his Florida congressional seat Friday, a day after he came under scrutiny for sending questionable e-mails to a 16-year-old boy. He left office, effective immediately, hours after he was confronted with sexually explicit Internet instant messages he exchanged with teens.

Foley, 52, had represented part of Palm Beach County and the Treasure Coast since 1995. As recently as this past spring, he contemplated seeking the Republican nomination for U.S. Senate. His downfall hands Republicans a political mess, making it more difficult for the party to keep control of the House.

A hallmark of his career as a congressman was his fight against child sexual abuse and child pornography. As co-chairman of the House Caucus on Missing and Exploited Children, he bragged in 2005 about legislation he wrote that overhauled national sex offender registration and notification laws.

Six hours after Foley’s resignation letter was read to the House by a clerk, the chairman of a panel that oversees the page program issued a one-page written statement that deflected any blame from House leaders.

The statement from Rep. John Shimkus, R-Ill., said the House Page Board he chairs investigated the allegations late last year, but he said Foley “was not honest” in denying improper conduct with the teenager. Pages are high school students who attend classes under congressional supervision and work as messengers.

In a three-sentence public statement, Foley said it was an honor to serve in Congress for 12 years. He didn’t offer a reason for his resignation. “I am deeply sorry and I apologize for letting down my family and the people of Florida I have had the privilege to represent,” Foley said.

The developments sent shockwaves through the Florida and Washington political worlds.

“I am literally speechless,” said Rand Hoch, a former chairman of the Palm Beach County Democratic Party who has known Foley for almost 20 years.

Sid Dinerstein, chairman of the Palm Beach County Republican Party, defended Foley and attacked critics early Friday afternoon before the sexually explicit Internet messages became public – then expressed betrayal after the sordid details and resignation came out.

“We don’t defend the indefensible,” he said. “In the four years I’ve been chairman, this is the first day I’m not happy about it.”

The potential for criminal prosecution of Foley is not clear.

Robert Jarvis, a Nova Southeastern University Law School professor in Davie, said that after reading the Internet message conversation between Foley and the teenager that it could be argued a crime occurred.

“The difficult problem in most of these cases (is the question) “Is there a solicitation for sex?”‘ Jarvis said. He said that it could be argued Foley crossed that line with comments indicating a sexual interest in the teenager.

On Capitol Hill, U.S. Rep. Robert Wexler, D-Fla., said reactions included shock, anger and embarrassment for the institution of Congress. “People just have a real mix of emotions,” he said. “There is no glee when someone you know for many years finds himself in a terribly unfortunate circumstance.”

U.S. Rep. Clay Shaw, R-Fla., who also represents part of Palm Beach County and lives down the street from Foley in Washington – a location they call “Florida Row” – was harsh in his assessment.

“This type of behavior is what I try to protect my grandchildren from. It is unacceptable. He should have resigned. Members of Congress are responsible for protecting the most vulnerable among us – our children,” he said in a written statement.

Foley had been considered a shoo-in for a seventh term in Congress, and the contest is now wide open.

“Moral meltdowns are one of the things that usually drive people to another party,” said Susan MacManus, a University of South Florida political science professor in Tampa. The circumstances surrounding the resignation “make that district much more competitive and even leaning Democratic right now.”

For months, a Republican businessman turned Democrat, Tim Mahoney, has been waging an aggressive campaign for Foley’s job, with both sides running nasty TV attack ads.

Republicans immediately began calculating Friday who would be their party’s best hope for keeping the congressional seat in their hands, especially in an election season when Republicans are at risk of losing control of the House of Representatives. A switch of 15 seats would turn the House Democratic.

One negative for the Republicans: state officials said Friday that ballots were already being printed for the Nov. 7 election, and Foley’s name would remain on them. Any votes for him will go to the candidate the party picks as a replacement.

Possible candidates include Republican state Reps. Carl Domino of Jupiter and Gayle Harrell and Joe Negron of Stuart. Both Harrell and Negron have eyed Foley’s seat in the past.

Harrell could not be reached for comment on Friday. Domino said he wasn’t planning to run for Foley’s seat, but would think about it.

“If I were a betting man, I would think I wouldn’t do it,” he said. “But when all your friends are calling you and you’re on the top of their list to be a congressman, that’s pretty humbling.”

Negron said he planned to run.

“I think this seat is too important to hand it over to Tim Mahoney,” he said, adding that he’s already lined up support from key Republicans, including state Sens. Jeff Atwater, R-North Palm Beach, and Ken Pruitt, R-Port St. Lucie.

Negron decided not to run for re-election to the House this year so he could campaign for attorney general, but he dropped out before the primary.

In May 2003, as Foley was seeking his party’s nomination for the U.S. Senate, he accused Democrats of trying to damage his campaign by spreading rumors about his sexual orientation. During a news conference, Foley would not say if he was gay, calling the question “highly inappropriate.”

Three months later, he said he needed to spend time with his father, who was battling cancer, and dropped out of the Senate race. U.S. Sen. Mel Martinez, R-Fla., won the seat.

Rep. Robert Wexler, D-Fla., has known Foley for close to two decades. Both were young men making their mark in Palm Beach, state and national politics. Though they were frequent television sparring partners during the aftermath of the 2000 presidential election, the two were friends and worked together on issues.

Wexler said he spoke to Foley on Thursday night after voting was finished on the House floor.

“I just asked him how he was faring, and he certainly seemed preoccupied, and he was holding up as best he could through what I’m sure was very difficult circumstances,” Wexler said. “I certainly had no inkling that he was going to resign.”

The Associated Press contributed to this report.