WASHINGTON—The defences keep changing. The goalposts keep moving. And the saga of Donald Trump and Russian election interference keeps getting both more ridiculous and more serious.

This week’s sensational episode is a rare combination of cloak-and-dagger and Beavis and Butthead. The president’s clueless eldest son, a clueless British publicist and a Russian pop singer come together for a series of astoundingly indiscreet conversations in which the son declares, in writing, “I love it” when he’s offered incriminating information on Hillary Clinton from the Russian government . . . .

Laugh-out-loud farcical ineptitude. And yet the Watergate scandal also began with bumbling peripheral players caught red-handed. Junior’s errors make it seem more likely that the investigations into this scandal might discover something as damning as the probes into that one did.

Special counsel Robert Mueller, the former FBI director, has assembled a dream team of investigators with expertise in a wide range of wrongdoing, from money laundering to campaign finance violations. Until the New York Times began publishing its Donald Jr. scoops on Saturday, it was fashionable in Washington to speculate that Mueller would manage to find transgressions of some kind, just not collusion, itself.

The focus is squarely back on collusion.

There’s a lot we still don’t know. We do know, now, that the president’s eldest son was eager to accept covert Russian help — and that two of Trump’s other closest advisors were prepared to meet with someone who promised such help.

If Donald Trump Jr., son-in-law Jared Kushner and campaign chairman Paul Manafort were willing to take that bait, in what other ways were they willing to deal with the Russians?

If Donald Trump Jr. was so unsurprised by the publicist’s assertion that Russia was making an effort to “support” Trump, what previous conversations had the campaign held with the Russians?

And, now, as in 1973, the main question becomes: what did the president know and when did he know it?

The timeline sure is curious.

On June 7, Donald Trump Jr. set up the meeting for two days later. On that very same Wednesday, the senior Trump promised a bombshell speech, probably for the following Monday, about “all of the things have taken place with the Clintons.”

The speech never happened: a terrorist attacked Pulse nightclub the day before, and Trump spoke about that. But he had sounded like a man who thought he was about to come into possession of some dirt.

In a Wednesday interview with Reuters, Trump denied knowing that his son had held the meeting until a “couple of days ago.”

But speaking to reporters later that day on Air Force One, he cracked open the door a little bit: “Maybe it was mentioned at some point,” he said, but he didn’t know about the offer of Clinton information.

On this story, from these people, even the most categorical denials are no longer credible.

Time and again, “never happened” has morphed into “it happened, but not that way” to “it happened that way, fine, but there’s nothing wrong with it.”

And so, this week, the president’s declarative cries of “fake news” and “total hoax” have been replaced by defensive claims that such meetings are “very standard.”

It does not currently appear as if most Republicans care about the continued unravelling. Members of Congress brushed off questions. The Fox News cheering section tiptoed as artfully as ever to stay in step with dear leader. Trump voters delivered their usual standing-by-their-man indifference to local newspapers.

But Watergate also failed to budge Republicans for a time, and then a presidency vanished. Trump may serve eight years, for all we know now. More than ever, however, it seems that there is more to come.

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As if trying to prove that the story could get sillier, senior Trump advisor Kellyanne Conway went on Fox Wednesday and held up pieces of paper on which she crossed out the word “collusion” and pointed to the words “illusion” and “delusion.”

“What’s the conclusion? Collusion? No. We don’t have that yet.”

Conway was smiling.

But after the preceding four days, the “yet” sounded ominous.