In the early morning of Oct. 29, 1968, Walt Rostow, special assistant for national security affairs, handed President Lyndon B. Johnson a memo from his brother, Eugene, who was undersecretary for political affairs.

It reported that close associates of Richard Nixon told prominent banker Alexander Sachs that the GOP presidential nominee “was trying to frustrate the president” by “inciting Saigon to step up its demands” to scuttle the peace talks in Paris.

It was true. For months, members of the Nixon campaign led by Anna Chennault, with collusion from John Mitchell and John Tower (and likely Spiro Agnew), contacted South Vietnamese government officials and promised a better deal from Nixon. They, along with Nixon, feared a breakthrough in Paris might throw the hotly contested election to Democratic presidential nominee Hubert Humphrey.

An angry Johnson responded by gathering information through National Security Council intercepts of South Vietnamese telegrams, and FBI surveillance and wiretaps of Chennault.

Soon, LBJ declared to Sen. Everett Dirksen, “This is treason!”

He personally challenged Nixon, so much so that Nixon called on Nov. 3 to deny the charges.

Not convinced, Johnson weighed whether to expose the Nixon campaign’s duplicity.

Several factors shaped his deliberations. First, he had not campaigned for Humphrey and wanted to stay above the fray (following President Dwight D. Eisenhower’s example in 1960). To change course invited charges of partisanship.

Second, he feared outing his intelligence sources and admitting he used the FBI and NSC to monitor U.S. citizens and allies.

Finally, he worried about provoking a constitutional crisis so early in a Nixon presidency when it appeared he would likely win. Without definitive proof of Nixon’s complicity, he feared what might result from an investigation.

In the end, Johnson failed to expose Nixon, and Nixon won by a very narrow margin, leading one South Vietnamese official proudly to crow, “We helped elect an American president.”

Afterward, LBJ had Rostow take all the materials. They were dubbed the “X” file. They remained secret until 1994.

Nixon, on the other hand, ordered the break-in of the Brookings Institute in 1971 after a staffer reported incorrectly that the organization had materials on the matter. Ultimately, Watergate buried the story, but it remained an early example of the employment of dirty tricks, in this case to win an election.

The question is: What does the Chennault affair help us understand today?

The answers are obvious. Johnson’s fear of being seen as interfering in the election explains why it took time for the Obama administration to release the CIA and other intelligence agencies’ reports on Russian interference in the recent presidential election.

Obama worried about charges of partisanship. While obvious to many that the hacks and even fake news being generated only aided Donald Trump, to deliver such a bombshell would create a political minefield.

He also likely wanted to avoid revealing sources, both to protect them and prevent any speculation about how he obtained the information. He knew Hillary Clinton accusers U.S. Reps. Trey Gowdy and Jason Chaffetz would jump at the opportunity for another inquiry.

Finally, like Johnson, the White House probably feared creating a constitutional crisis for an administration even before it took office. Trump now enters having lost the popular vote by a significant margin and under the cloud of suspicion over foreign involvement to assist his victory. It was exactly the type of paralysis LBJ thought might unfold in 1969.

In the long term, this episode could resemble the Chennault affair. Nixon’s demand for the break-in of the Brookings Institute led to the creation of the “White House Plumbers,” and the rest is history.

Trump and his people likely will also circle the wagons, and the past shines light on what happens when that occurs.

Overall, the Obama decision might end like that of Johnson in allowing a crisis to develop that sets back the republic for years.

While LBJ did not live long enough to witness the embarrassing resignation of a president, Obama is young enough that his decision not to release the information in time will be judged for years.

Now, the question of external powers playing a role in shaping a presidential outcome remains the same: Who knew? Did collusion occur? How did it affect the results?

Both events just reinforce the idea: For all the things that change, they remain remarkably similar.