So, why did Nixon resign in the 70s again?
Nixon did not want to be the second President in US history to be impeached and the first to be convicted in the US Senate. At the point in time he resigned it was certain he would be impeached and almost certain he would be convicted in the Senate of perjury. He had lost support of the Republican leaders in the House and Senate due to the content of the tapes. By resigning he opened up the opportunity for the Ford pardon. Had the pardon not occurred he could have fought prosecution for years.
The Republican House and Senate leaders of the time were honorable men who defended their President until the evidence clearly demonstrated he had perjured himself. Ford was a patriot who knew a pardon would damage him politically but would end the nation’s long nightmare. It would have been difficult for Ford to govern if Nixon had been prosecuted in state and federal courts after resigning from office. The trials would have been on the nightly news for years and the Democrats would have used the spectacle to bludgeon Republican candidates for a decade. Ford likely lost his chance for reelection, but allowed the nation to move on. Nixon left office in disgrace and will be forever tarnished in the history books.
By the time Clinton was impeached, there was no honor in the leadership of the legislature. Clinton clearly perjured himself — lying directly to the American people on television about not having sex with Monica Lewinsky. There was likely evidence of other perjury and perhaps other crimes which was never released to the public but was available to Congress in the evidence room. However, the Democrat leadership stood by their man and the Republican Senate leadership had no desire to convict the President once he was impeached by the House. Possibly the FBI files in the President’s possession came into play. Whatever the reason, the Dems rallied around their man and the Republicans didn’t have the backbone to conduct a trial in the Senate where other evidence of wrongdoing could have been exposed such as illegal campaign donations by the Chinese.