In a furious exchange on the floor of the house on Thursday, the Democratic Speaker, Tom Foley, denied a Republican accusation that he had solicited the US attorney in charge of the case to ask for secret documents not to be publicly released. Mr Foley said the Republicans were engaged in 'broad-brush insinuations and accusations'.
Evidence that the Democratic leadership in Congress is involved in petty corruption would be extremely damaging for the Democrats in the 1994 election. Their reputation is already battered by the House Bank scandal during which it was revealed that Congressmen had regularly cashed cheques on their own bank which subsequently bounced.
Mr Rostenkowski was also accused yesterday of trying to delay the guilty plea agreement struck by Robert Rota, the former house postmaster, with the government, until after he had finished negotiations with the Senate on President Clinton's dollars 500bn ( pounds 333bn) economic package. If he is indicted he will have to step down as chairman of the Ways and Means committee, which holds sway over the tax code, trade law, health care and welfare.
Investigation of the House post office has been going on for two years but only exploded into a political scandal this week when Mr Rota pleaded guilty to embezzlement. He is co-operating with the government in making a case against Mr Rostenkowski for embezzling dollars 21,300 and Joe Kolter, a former Congressman from Pennsylvania, for taking dollars 9,300.
In the late 1980s the Democratic majority in the House was badly damaged when the Speaker, Jim Wright, and Tony Coelho, one of their most effective leaders, were forced out of office by the savings and loans scandal. The post office scandal has developed just as the Democrats had hoped to escape their reputation for venality.
Mr Rostenkowski is refusing to say anything about the allegation that he embezzled dollars 21,300 from his office expense account by purporting to spend the money through the House post office. But the accusation has gained credibility because he had the reputation for taking all the perks available to a member of Congress.
In 1990 and 1991 Mr Rostenkowski used nearly a third of the dollars 358,000 spent by his campaign and political action committee on such items as travel, chauffeurs and rental payments to himself. Dinners alone cost dollars 33,000 over two years or an average of dollars 300 a week. At the same time Mr Rostenkowski has only a small one-bed room apartment in Washington and has argued for banning honoraria but raising Congressmen's salaries to dollars 135,000 a year.