We know this much of the story. But this is a case where the particularity of the story, the minutiae of intelligence officials' denials, discussions of what authority a president might theoretically have to do such a thing all conspire together to confuse rather than illuminate what happened.
The real story here is that the President, by force of his office and audacity, was able to inject into the national conversation a preposterous claim which the country has spent two weeks debating. True, most people may not believe it. But virtually everyone has gone through the motions of probing the question as though they might be true. Intelligence communities have been briefed, statements have been made, a number of news conferences have been dominated by it. Perhaps most notably, members of his party have only been willing to say that there is as yet no evidence to back up the President's claims - not that they are obviously false and represent a major problem in themselves.
I would say that this ability - both the President's pathological lying and our institutions' inability to grapple with it - is the big, big story. The particulars of the accusation basically pale in comparison.
Also note how these lies have spread. The need to perpetuate the lie has made it necessary to escalate it. In an attempt to work around the uniform denials of every US government agency that does 'wire-taps', Press Secretary Sean Spicer was forced to grasp on to the rantings of a Fox News 'legal analyst' who claimed that President Obama had used British intelligence to sidestep US legal strictures. Repeating this claim with the imprimatur of the White House triggered a minor but real diplomatic incident with the United Kingdom, which may not yet be settled.
Continuing to defend the baseless claim required Trump to revisit the story in his press conference with German Chancellor Angela Merkel, both doubling down on the claim and also passing the buck to Fox News and creating the surreal spectacle of suggesting that he, like Merkel, was the victim of the very intelligence services and law enforcement agencies which he in fact now leads.
While most have dismissed the President's claims, it is still the case that he has been allowed to drive public debate for two weeks over an obvious lie. Members of his party will not denounce it as a lie or even obviously false. That's a big problem. Without being overly dramatic, this is a warning case of people in power deciding what's true and false which is a harbinger of free government dying.