Former Trump campaign manager Paul Manafort departs U.S. District Court in Washington on Feb. 28. (Yuri Gripas/Reuters)
Shane O’Sullivan is a documentary filmmaker, senior lecturer in filmmaking at Kingston University, London and author of the new book, “Dirty Tricks: Nixon, Watergate and the CIA."

While the special counsel could not establish collusion between the Trump campaign and the Russian government in its hacking of Clinton campaign and Democratic National Committee emails, questions remain about the ties between President Trump’s former campaign chairman, Paul Manafort, and Russian actors during the 2016 election.

Manafort has been sentenced to 7½ years in prison for bank fraud, tax fraud and conspiracy. But we still don’t know why he gave polling data to an alleged Russian spy during the campaign; how his lobbying for a pro-Russian political party in Ukraine shaped changes to the Republican platform on Ukraine that favored Russia; or how his ties to an oligarch close to Russian President Vladimir Putin influenced the decision to the lift sanctions on three firms linked to him.

Moreover, the 50 hours Manafort spent supposedly “cooperating” with the Mueller investigation produced little of value, and he breached his plea agreement by lying repeatedly to Mueller’s office and the FBI.

Manafort’s case recalls the dramatic fall from grace of John Mitchell, Richard M. Nixon’s campaign director during the 1968 and 1972 elections. At the height of the Watergate crisis, Nixon encouraged Mitchell to “step forward” and take the blame to protect the White House, hinting at a future pardon — the motive some ascribe to Manafort’s refusal to “flip” on Trump.

In 1968, Mitchell colluded with a foreign power to win the election and got away with it. Four years later, Mitchell approved Operation Gemstone, a secret intelligence-gathering effort targeting Democratic presidential candidates, which led to the infamous Watergate break-ins at DNC headquarters.

Desperate to win the 1972 election at all costs, Mitchell played a key role in the Watergate coverup and was later convicted of obstruction of justice, making false statements to the FBI and a grand jury, and committing perjury before the Senate Watergate Committee. He was sentenced to 2½ years to eight years in prison but served just 19 months.

The story of Mitchell’s fall illustrates how conspirators in a political coverup turn on one another when former colleagues start cooperating with prosecutors. Cover stories fall apart, and loyal allies like Mitchell are sacrificed to protect those higher up the chain of command.

Mitchell’s illegal activities began during the 1968 campaign when he worked with Anna Chennault, a key member of the “China Lobby,” to collude with the South Vietnamese government to postpone peace talks until after the election, helping Nixon secure the presidency.

Mitchell first met Chennault in February 1968, when she brought the South Vietnamese ambassador, Bui Diem, to Nixon’s New York apartment to meet senior campaign staff, just weeks after Nixon announced his candidacy. At a top-secret meeting in July, Diem met Nixon himself in the presence of Mitchell and Chennault, and thereafter, Chennault was in daily contact with Mitchell right up to the election.

In the last week of the 1968 campaign, through NSA intercepts and FBI surveillance, President Lyndon B. Johnson discovered the Nixon camp’s subterfuge and attempts to undermine the peace talks. After much agonizing, he decided he couldn’t expose Nixon’s duplicity by going public with classified intelligence reports. That decision cost the Democratic candidate, Hubert Humphrey, the election; Nixon squeaked home by less than 1 percent of the popular vote.

After Nixon’s inauguration, he appointed Mitchell as attorney general, the chief law enforcement officer in the country, despite his treasonous attempts — approved by Nixon — to undermine peace negotiations in Paris to end the war in Vietnam. More than 21,000 American lives were lost in Vietnam during Nixon’s presidency.

On March 1, 1972, Mitchell resigned his position as attorney general to run Nixon’s reelection campaign through the Committee to Re-Elect the President. At the end of that month, he approved a budget of $250,000 for Operation Gemstone, a series of secret and illegal intelligence-gathering programs run by Nixon intelligence operative Gordon Liddy. The two main targets: the headquarters of George McGovern, the antiwar candidate who went on to win the Democratic nomination, and the offices of the DNC at the Watergate.

In late May, the Watergate burglars broke into DNC headquarters to plant bugs on the phones of Democratic officials and search for (and photograph) documents potentially showing alleged Cuban sponsorship of the McGovern campaign.

Disappointed by “the fruits” of the first break-in, Mitchell’s deputy, Jeb Magruder, sent the burglars in a second time on June 17, 1972, to photograph more documents and fix a faulty bug. This time, they were caught. One of the men arrested, James McCord, was head of security for the Committee to Re-Elect the President and directly linked the burglars to the Nixon campaign. When Mitchell heard the news, he dispatched Liddy to ask Attorney General Richard Kleindienst (his former deputy) to secure McCord’s release. To his credit, Kleindienst refused.

A few weeks later, Mitchell resigned as campaign director for “personal reasons” — to care for his increasingly erratic wife, Martha, an alcoholic now cracking under the strain of the Watergate investigation. But Mitchell continued to play a key role in the coverup.

In August 1972, when his former deputy, Magruder, was called to testify before the grand jury, Mitchell and White House counsel John Dean helped Magruder create a cover story to conceal his involvement in the break-ins. It worked, at least for a while. The Watergate indictments went no higher than Liddy, and Nixon was reelected in a landslide, untainted by any direct connection to the burglars.

By April 1973, however, as Dean and Magruder began cooperating with prosecutors, Nixon was desperate. In a taped conversation on April 14, the president met with senior advisers H.R. Haldeman and John Ehrlichman to discuss how Mitchell and Magruder could be persuaded to “step forward” to assume responsibility for the break-ins and deny any White House involvement.

Nixon floated future pardons by instructing Ehrlichman to tell them “the president holds great affection for you and your family.” But within weeks, the plan unraveled and Haldeman, Ehrlichman and Dean resigned.

After Nixon’s resignation in August 1974, Mitchell became the first attorney general of the United States to face a criminal trial. Throughout his testimony and right up to his death in the late 1980s, Mitchell denied approving the Watergate break-ins or seeing any of the intelligence gleaned by the Watergate burglars. He insisted his only crime was his loyalty to the president, withholding evidence of the Watergate coverup from investigators to protect Nixon’s reelection bid above all else.

Despite Mitchell’s denials, the jury found him guilty on six counts and sent him to prison.

While John Mitchell got away with collusion with a foreign power in 1968, his systematic lying to cover up the DNC “hack” in 1972 was eventually uncovered when Dean and Magruder started cooperating with prosecutors. Nixon and senior White House aides were soon willing to sacrifice Mitchell to save themselves. They played on Mitchell’s loyalty and floated a future pardon. (Ultimately, it was Nixon who was pardoned, while key staff members went to jail.)

Judge Amy Berman Jackson recently sentenced Paul Manafort and set a November trial date for Roger Stone, the self-styled “dirty trickster” with whom Manafort started his lobbying career in 1980. Stone has pleaded not guilty to charges similar to those John Mitchell faced: obstruction of justice, lying to Congress and suborning false testimony.

While Manafort begins serving his sentence for other crimes, his loyalty to Donald Trump and refusal to “flip” may account for Robert S. Mueller III’s failure to establish collusion. Mitchell’s obstruction of justice got Nixon reelected but couldn’t save his presidency. As Manafort and Stone face further prosecution, we still don’t know how deep their alleged obstruction of justice goes or where it will lead, or how long they will stay loyal to the president.