When The New York Times reported the resignation of Mr. Flynn as President Trump's national security adviser, February 14, 2017, it referred to "a transcript of a wiretapped conversation" between Mr. Flynn and Ambassador Kislyak.  The next day, the Times reported that the circumstances leading to the Flynn resignation "traced back to a call last December between Mr. Flynn, then on tap to become Mr. Trump's national security adviser, and Sergey I. Kisylak, the Russian ambassador to the United States." 

Another Times account went on to report: "Obama advisers heard separately from the F.B.I about Mr. Flynn's conversation with Mr. Kisylak, whose calls were routinely monitored by American intelligence agencies that track Russia diplomats."  Obama officials were said to be concerned that Russia was offered a quid pro quo if it would not respond to the expulsion of 35 Russian diplomats and added sanctions, based on allegations that Russia meddled in the presidential election.  The FBI, the Times reported, said there had been no quid pro quo offered.  The Times then noted that Washington Post columnist David Ignatius, January 12, 2017, had reported on Mr. Flynn's contact with the Russian ambassador.  How did Mr. Ignatius obtain his information if not by unlawful leak?

Kimberley A. Strassel pointed out in her Wall Street Journal column, April 7, 2017 ("The Conflicts of J. Edgar Comey"), that it is a felony to leak "highly classified about a conversation between a presidential adviser and a foreign official" to the press.  Ms. Strassel was right in informing readers that those responsible for leaking the details of a wiretapped conversation between Mr. Flynn and Ambassador Kisylak could face as much as "10 years in federal prison."

The unmasking of Mr. Flynn is, alas, not the only case of unmasking of Trump aides by outgoing Obama officials.  There is now, famously, the matter of unmasking of Trump people by Obama national security adviser Susan Rice and by Samantha Power, President Obama's ambassador to the U.N.

It is, alas, understandable that a media hostile to President Trump, will ignore violations of federal law when the purpose of such violations is, apparently, the overthrow of the Trump presidency.  What of the principle that "no one is above the law" – not even fanatical NeverTrumps?

It would be foolhardy to consider that Special Counsel Robert Mueller will probe anti-Trump leaks that not only violate U.S. law, but could harm national security, but Attorney General Sessions has the responsibility to uphold the rule of law – and defend the Constitution against all enemies, foreign and domestic.

Wall Street Journal columnist Holman W. Jenkins, Jr., December 2-3, concluding his column "The Media's Flynn-sanity," observed:

After the Trump election, the direction of the causation in the ensuing Russia scandal in my judgment seems fairly clear. The media and bureaucracy reject Mr. Trump not because they got wind of Russia. They were determined to reject Mr. Trump and Russia was handy.

But in our free republic, it is the people – not self-promoting would-be elitists – who hold sovereign power, and the people, by constitutional process, elected Donald J. Trump our president.  Mr. Sessions must stand with the people; stand with the Constitution; and, yes, stand with President Trump against all who would make a mockery of our sovereignty.  He must investigate and prosecute the individuals responsible for the unlawful unmasking of Gen. Flynn any other Trump aides.

Thomas Lifson adds:

I have to wonder if the leaker might be the guy who seems to have had his hand in everything involving the effort to unseat the duly elected president, Peter Strzok.  If he could be identified as the leaker, then the classic prosecutor's pattern being followed by Mueller with Flynn could be turned against him: squeeze him with the threat of prison to get him to squeal and implicate the higher-ups.  I understand that ex-law enforcement people do not do very well in prison.  At this point, it is a fantasy, but Strzok seems to have been a busy beaver when it comes to politicized activity.