The bottom appears to have dropped out from under scandal-plagued Rep. Tim Mahoney (D-Fla.).

A new Republican poll released Friday morning showed Mahoney — the subject of a sex scandal that broke earlier in the week — badly trailing his GOP challenger, attorney and Pittsburgh Steelers heir Tom Rooney.

The poll of 300 likely voters, taken Wednesday and Thursday, showed Rooney with 55 percent of the vote and Mahoney with 29 percent. Taken by the Tarrance Group for Rooney and the National Republican Congressional Committee, the survey had a 5.8-point margin of error.

Mahoney, who owed his election in 2006 to the sex scandal surrounding his predecessor, ex-Rep. Mark Foley (R), was already in a tough race with Rooney, but internal Democratic polls taken earlier in the month showed him with a significant lead.

But after ABC News reported Monday that Mahoney had had an affair with an ex-staffer and then had attempted to buy her silence, the Congressman’s political standing fell precipitously. The Democratic Congressional Campaign Committee has stopped spending money on his re-election, and party leaders have essentially written the seat off.

“Mahoney’s scandal has completely destroyed him as a credible candidate, and he is not able to compete in this election,” GOP pollster Dave Sackett wrote in a memo to Rooney and the NRCC.

There remains the possibility that Mahoney will resign or abandon his re-election bid, but even if he did pull out of the race, his name would remain on the ballot — which is exactly what happened two years ago when the Foley scandal unfolded — and state Democratic leaders would designate someone as his replacement.

But considering that the Tarrance Group poll showed that 87 percent of the district’s voters were fully aware of the scandal, any Democrat running to replace Mahoney would likely be doomed by his troubles.