President Trump's national security adviser Michael Flynn resigned Feb. 13 after revelations that he had discussed sanctions on Russia with the Russian ambassador to the U.S. prior to Trump taking office. Here's what you need to know. (Deirdra O'Regan/The Washington Post)

President Trump’s national security adviser, retired lieutenant general Michael Flynn, resigned Monday night after “inadvertently brief[ing] the Vice President Elect and others with incomplete information regarding my phone calls with the Russian Ambassador [Sergei Kislyak].” Flynn resigned not because of his communications with the Russians, but rather because of his lack of discretion, misleading Vice President Pence about the nature of the exchanges, and, allegedly, opening himself up to blackmail by the Russians.

I wrote previously that back-channel contacts between Washington and Moscow are hardly unprecedented, either before presidential elections or during the transition period when power shifts from one party to another in the United States. The case of Richard Nixon in 1968-1969 furnished several clear examples of back-channel contacts, including exchanges between Nixon’s national security adviser, Henry Kissinger, and an identified KGB operative, Boris Sedov.

The differences show why the Nixon-Kissinger back channels were successful while Flynn resigned after less than three weeks.

First, Nixon and Kissinger synchronized the two back channels to the Soviets during the 1968 election and the transition period. This included the Kissinger-Sedov channel and also one between Nixon’s adviser and later ambassador to NATO, Robert Ellsworth, and the Soviet charge d’affaires, Yuri Cherniakov. Kissinger and Ellsworth acted with Nixon’s knowledge and the messages both men conveyed to the Soviets complemented and reinforced each other.

We know these details not because of the content of reportedly leaked FBI wiretaps, as in the case of Flynn, but because of good record keeping. Kissinger wrote detailed memorandums of his various back-channel exchanges and shared them with the president (and, occasionally, others who had a need to know). In Washington, political warfare is frequently fought on the battlefield of competing memorandums. Kissinger also had his staff make transcripts of his phone conversations, eventually off recordings of the calls, but initially by having a secretary write in shorthand by listening on a telephone with a muted microphone.

By contrast, Flynn’s inconsistency over the content of his conversations with Kislyak hurt his credibility and brought on scrutiny both inside and outside the White House.

Somewhat strangely for a career intelligence officer, Flynn also used insecure means of communication by talking on open telephone lines to Kislyak. In military-speak, he used poor communications security (COMSEC), which was apparently subject to FBI monitoring — and, hypothetically, foreign intelligence collection.

Kissinger and Ellsworth met in person with their Soviet interlocutors. While in-person meetings are subject to surveillance, it’s a great deal more complicated legally and technically than monitoring open phone lines.

Flynn’s preference for the phone is ironic since Trump said a few weeks ago, “You know, if you have something really important, write it out and have it delivered by courier, the old-fashioned way.”

Of course, 2016-2017 is not 1968-1969. In 1968, the Russians did not conduct a campaign to discredit or influence the outcome of the U.S. election. None of the major candidates in the election — Nixon, Hubert Humphrey and George Wallace — nor their advisers had business ties to the Soviet Union. Nixon won a plurality of the popular vote and was not prey to charges of being an illegitimate president.

In 2016-2017, Russia is a more controversial topic because of Moscow’s activities during the U.S. election, in Syria, Ukraine and elsewhere. Flynn reportedly discussed sanctions that the United States, under the then-outgoing Obama administration, imposed on Russia for Moscow’s interference during the presidential campaign.

Although Flynn may not have explicitly conveyed a quid pro quo — specifically, that the Russians would not respond strongly to the sanctions, and the incoming Trump administration would work on removing them — the episode demonstrates the importance of back-channel actors maintaining the confidence of the leaders they represent.

Kissinger worked to validate his role as a back-channel intermediary to the Soviets and he made sure Nixon put his imprimatur on the exchanges. Kissinger kept good records and he kept his boss, Nixon, informed. Fundamentally, back channels require the confidence of the person at the top. Kissinger understood this and became the indispensable man for Nixon’s foreign policy.

Flynn clearly lost the confidence of those at the top and had to go.

Richard A. Moss is an associate research professor, co-director of the Halsey Bravo research effort, and a faculty affiliate in the Russia Maritime Studies Institute at the U.S. Naval War College’s Center for Naval Warfare Studies. The University Press of Kentucky published his book, “Nixon’s Back Channel to Moscow: Confidential Diplomacy and Détente,” in January 2017.

Author’s note: The thoughts and opinions expressed in this publication are those of the author and are not necessarily those of the U.S. government, the U.S. Department of the Navy or the Naval War College.