If there was a consensus among Democratic candidates, it was that Massachusetts Gov. Michael S. Dukakis had the most money and the best campaign manager, a short, dark, organizational genius named John Sasso. Monday night, once again, Dukakis raised $1 million. But two days later he lost Sasso, and Democrats are asking, "What's left?"

The sad story begins, as does so much contemporary political history, with a tape. This was a reel splicing together a fiery campaign commercial featuring British Labor leader Neil Kinnock and a debate appearance by Sen. Joseph R. Biden Jr. (D-Del.) in which he repeated Kinnock's words without attribution.

Time magazine said this week that the Dukakis campaign had given the tapes to The New York Times, the Des Moines Register and NBC News.

On Monday, Dukakis, flaunting his reputation for squeaky-cleanness, said at a news conference that he would be "astonished" and "very, very angry" if anyone in his campaign had engaged in "negative campaigning."

But yesterday, the governor had belatedly learned the truth and accepted, with obvious reluctance, Sasso's resignation. Paul Tully, his political director, went, too.

It was a bad day for Dukakis, a bad day for Democrats, a bad day for politics. On Capitol Hill, there was wonder and dismay.

The relationship between Dukakis and his onetime chief of staff was special in that Sasso was, as one glum aide said, "the soul and engine of the campaign." Sasso, who cut his teeth in national politics by managing with considerable skill the troubled vice-presidential campaign of Geraldine A. Ferraro, had let it be known for months that he would leave Dukakis if he didn't try for the presidency. He was widely credited with persuading the governor to take the plunge. He recruited a crack staff, engaged a peerless fund-raiser, managed everything from who would ride in the governor's car to how to win the South. Said his friend Tom Vallely, one of the few Massachusetts politicos who went with Biden, "John is a commander." No campaign manager had more fans in the news media. His trump card was straightforwardness.

He seems to have leaked the tape because he had it. "It was cockiness," said a grim friend. Sasso is 40 years old; his candidate was running strong.

"Why did he go after somebody who wasn't going anywhere?" asked one Democratic senator.

The speculation is that Sasso did not mean to knock Biden out of the race, only to give him a good poke because he was asking for it.

Only the purest -- and these include Dukakis -- would say that giving out a tape of a rival stealing a Welshman's words is particularly reprehensible. After all, Biden borrowed Kinnock's impassioned words about being the first member of his family to go to college in a public forum. Thousands of people in the auditorium heard him; millions more on television. It wasn't gossip or innuendo or boudoir secrets.

By itself the two-track tape would have been an embarrassment to Biden. But its publication stirred other disclosures -- that Biden lied about his academic record at a New Hampshire meeting, that he had plagiarized in his freshman year in law school. The accumulation toppled a shaky campaign.

The timing of the strike was a matter of some resentment in the party. Democrats savaging other Democrats is not considered cricket, especially when Biden was chairing the confirmation hearings of Supreme Court nominee Robert H. Bork, who offends large chunks of the Democratic constituency.

What was unforgivable was that Sasso did not, even when the Time story was brewing, tell his candidate what he had done. He let him go to a news conference and expose himself to ridicule and humiliation. Dukakis, inadvertently upping the ante, was at his most self-righteous in proclaiming his intolerance for "negative campaigning."

Dukakis was allowed to take the ax to the twin pillars of his candidacy -- honesty and competence. In the light of what occurred, Dukakis was seen to be either lying or not knowing what was going on. For a critic of President Reagan's "hands-off" style of management, it was a bad fall.

To be done in by his campaign manager was the last thing anyone expected of Dukakis. Sasso was regarded as a paragon of loyalty. Dukakis refused initially to accept his resignation. He is the first victim of the character issue by association.

Dukakis is now bereft of his two principal political operatives. He still has the money; he still has the record of economic miracle and a 3 percent unemployment rate. But the heart of his campaign has been removed, and a transplant seems unlikely.