WASHINGTON – Congressional Democrats reclaimed control of Congress in 2006 by pledging to “drain the swamp” after Republican ethics scandals rocked the Capitol. Now, a series of controversies involving Democratic members has robbed the party of its claim to hold the higher moral ground – and could threaten its hold on power in this fall’s elections.

Friday’s announcement by Rep. Eric Massa, D-N.Y., that he will resign amid allegations that he sexually harassed a male staffer capped a week of near-daily ethical distractions for a party struggling to pass heath-care reform legislation.

A few days earlier, congressional Democrats forced Rep. Charles Rangel, D-N.Y., to step down temporarily from the chairmanship of the House Ways and Means Committee. The House ethics committee admonished Rangel for accepting corporate-sponsored trips, and he remains under investigation for other alleged violations. Rep. Pete Visclosky, D-Ind., is under investigation by the Justice Department.

The controversies have increased Republican attacks on House Speaker Nancy Pelosi, Calif., who pledged in 2006 that Democrats would run “the most ethical Congress in history.”

While not yet as severe, the Democrats’ ethics controversies resemble those of the Republicans when they held the majority in 2006. Connections to disgraced lobbyist Jack Abramoff led to resignations and even prison; House Majority Leader Tom DeLay, Texas, resigned his post amid investigations of his staff, and Rep. Mark Foley, Fla., resigned after sending sexually suggestive Internet messages to congressional pages. Exit polls showed that those ethics controversies played a role in the GOP losing control of Congress.

“Ethics really matters to voters; they matter almost more than any other issue,” said Melanie Sloane, head of the nonpartisan Citizens for Responsibility and Ethics in Washington. “And you would think that both parties would know that, because Democrats lost in 1994 and Republicans lost in 2006 because of it.”

Massa said he would step down from his upstate New York seat on Monday in part to stop an ethics investigation that he said “would tear my family and my staff apart.” He had previously said he would step down at the end of the year for health reasons after a recurrence of non-Hodgkin’s lymphoma.

“There is no doubt in my mind that I did in fact, use language in the privacy of my own home and in my inner office that, after 24 years in the Navy, might make a Chief Petty Officer feel uncomfortable,” Massa said in a statement Friday on his Web site. “In fact, there is no doubt that this ethics issue is my fault and mine alone.”

“It’s not that I can fight or beat these allegations, I’m guilty,” Massa told his Washington and campaign staff in a separate statement, which was reported by his hometown newspaper, the Corning Leader.

Congressional Republicans, while not highlighting Massa’s situation, said the controversies surrounding Democrats proved the party had done little to change the culture of Washington.

“Nancy Pelosi’s ‘most ethical Congress in history’ has been reduced to a punch line. Democrats are treading water in the very swamp they promised to drain,” said Ken Spain, a spokesman for the National Republican Congressional Committee, the campaign arm of House Republicans.

Pelosi defended Democrats, noting that the party had established an outside committee to investigate allegations against lawmakers. The complaints are then forwarded to the formal ethics committee, which is composed of House members. “I think we have come a long way since I became speaker,” she said Thursday.

Republicans have had their own controversies, including Sen. John Ensign, Nev., who stepped down from a Senate GOP leadership position in July after admitting an affair with a former campaign staffer. He faces a congressional investigation over his role in finding the husband of his mistress a job.