On the face of it, it seems at odds with basic logic.

How did a payment seemingly deemed perfectly legal while in the hands of the giver — in this case, the Prime Minister's former chief of staff, Nigel Wright, who lost his job over the controversy — turn into an alleged bribe the instant it found its way to the recipient, Senator Mike Duffy?

A definitive answer to that question will likely have to wait until the case against Duffy goes to court. We may get a better idea of the extenuating circumstances that led to charges against Duffy but not against the man who gave him the $90,000 to cover expenses that were under review and later deemed inappropriate when documents associated with the case are released.

In April, the RCMP effectively cleared Wright of criminal wrongdoing related to what they described at the time as "the gifting of $90,000" to Duffy.

"Upon completion of the investigation," the force said in a statement, "we have concluded that the evidence gathered does not support criminal charges against Mr. Wright."

That suggests the Mounties may have been persuaded that Wright's actions failed to meet the threshold for intent needed to lay charges related to "bribery of judicial officers," which requires that an offer be made "corruptly," a term that, somewhat unhelpfully, isn't explicitly defined in law.

The use of the word "gifting" in the earlier release, when read with hindsight, would seem to hint at such a determination.

A gift, after all, is freely given, with no strings — or, to use the parlance of Section 119(1) of the Criminal Code, no requirement that something that has or is to be "done or omitted by that person in their official capacity."

That still doesn't entirely explain how accepting such a gift could be done corruptly, but at least it provides a possible basis for the markedly differing interpretations of the motivation behind those on either side of that fateful transaction.

Indeed, retired parliamentary law clerk Rob Walsh told CBC News last fall that it was unlikely Wright would face charges over the payment.

"What benefit did Duffy give to Wright in exchange for the $90,000?  That Duffy make no further media comments? This is not a benefit to Wright," he pointed out via email.

"The funds were given to Duffy to bring the Duffy expenses controversy to an end, like settling a lawsuit. This is not fraud, nor is it breach of trust."

"I don't see any of this supporting criminal charges," Walsh concluded. 

"It's just self-serving politics."

In any case, from the perspective of the prime minister and his party, that version of events, while not ideal, is several orders of political magnitude better than the alternative — namely, having one or more senior staffers, past or present, join Duffy on the docket.

But it could also put Harper — and, potentially, other sitting parliamentarians, particularly on the Senate side, as well as current and former staffers — on the long list of potential witnesses who could be called upon when the case goes to trial. Sources say Wright has been advised to be ready to make himself available.

It's clear from Duffy's lawyer's preemptive response to the charges that the one-time star of the Conservative fundraising circuit believes the best defence is a good offence, and is training his sights on both the prime minister and his inner circle.

Given that strategy, there's little reason to think Duffy won't take the next step, and attempt to embarrass both the PM and the Conservative Party by challenging Harper to answer questions under oath.

MPs can't be forced to testify

In theory, parliamentary privilege grants all members of Parliament (which includes both MPs and senators, for the record) a blanket exemption from testifying in court in any trial — civil, criminal or even military court — when the House is in session, or within 40 days of dissolution or the opening of a new Parliament.

But as noted in the oft-cited procedural bible, otherwise known as House of Commons Procedure and Practice, "this claim is not intended to be used to impede the course of justice and, therefore, is regularly waived, particularly for criminal cases."

Practically speaking, it's difficult to envision a scenario where the political risk of appearing in court as a witness for either the prosecution or the defence would outweigh the optics of publicly refusing to do so.

It could also give the defence more leeway to put forward an alternate theory without fear of being contradicted from the witness box

Then again, given how slowly the wheels of justice can grind, it's entirely possible that such a request could come on the eve — or even in the midst — of an election campaign, in which case it would be hard to fault any elected official keen to remain that way from exercising his or her privilege.

Still, for the Conservatives, even though it may seem as though the eye of the Duffy storm has moved on from both the prime minister and his office, it may be more difficult to persuade the public to do the same with its collective outrage over the ongoing Senate expense scandal.

Although Wright may be free and clear of charges, the case still involves alleged acts that Harper has officially declared to be "disgraceful," committed by someone he personally recommended for appointment to the Upper House.

From their respective responses to Thursday's announcement, it's clear the opposition parties intend to make sure no one — or, at least, no undecided voter — forgets that.