Mark Foley was forced to resign on Friday after the publication of suggestive e-mails and other lewd messages that he had sent to a 16-year-old congressional intern. In one message, the Florida Republican, using an AOL account name of Maf54, tells him to “strip down” and, when told the teenager is wearing a T-shirt and shorts, he replies, “love to slip them off of you”. Capitol police have sealed his office and criminal charges are expected. Mr Foley, 52, who had previously ducked rumours about his sexuality, pioneered legislation against adults who prey on vulnerable young people. He had even helped to set up a hotline for parents and teenagers to tell police about “online child sexual exploitation”.

As recently as July 27, President Bush had hailed Mr Foley and other legislators behind child protection laws as being part of a “SWAT team for kids”.

On Saturday night the House Republican leadership issued a statement that condemned the communications between Mr Foley and the former pageboy as “unacceptable and abhorrent”. It said that it was reviewing rules governing contact with pages, announced that a freephone number was being set up for interns and parents to report concerns and promised an ethics committee investigation.

The Democratic Party has, however, seized upon evidence that the House leadership was warned about Mr Foley’s activities months ago, alleging that it sought to cover them up for fear of losing his seat in November’s mid-term elections. The Democrats are linking the case to a “pattern of corruption” in the Republican Congress and have called for an inquiry.

Over the weekend Republican Thomas Reynolds admitted that he had told Dennis Hastert, the Speaker of the House, as long ago as last year that a page’s parents had complained about inappropriate messages being sent by Mr Foley. Mr Hastert said that he did not remember this conversation but his office had nonetheless referred the matter to the clerk of the House.

The clerk passed the issue on to John Shimkus, who oversees the 200-year-old congressional page programme, which allows 72 high school juniors to work in the House for a session, answering telephones and delivering mail. It had been more than 20 years since the last scandal, when two congressman were censured for having affairs with pages, and Mr Shimkus believed that there was “no smoking gun here”. Instead, he said, Mr Foley had merely been told: “Stay away from this kid. This doesn’t look good.”

The congressman had been expected to hold Florida’s 16th District easily on November 7 — when the Democrats need a net gain of 15 seats to recapture the House for the first time since 1994. The Republicans will select a new candidate today, but the scandal has broken too late to stop Mr Foley’s name appearing as their nominee on the ballot paper, leaving the Democrat, Tim Mahoney, favourite to capture the district.

At a campaign rally on Saturday he said: “The Republican leadership team has been well aware of this problem with the pages for well over a year. It looks to me that it was more important to hang on to a seat and hold on to power than to take care of our children.”

Dan Bartlett, the White House counsellor, sought to distance the President from any damage, saying yesterday: “We learnt [about this] when the American people learnt. We are deeply shocked. We are glad there will be an investigation.”

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