Now that Donald Trump Jr.’s emails reveal that the Trump campaign welcomed election interference by the Russians (“I love it,” Junior enthused at the promise of receiving intel on candidate Hillary Clinton from a Kremlin-linked source), it might be a good time to turn the spotlight back to Donald Trump and whether his actions since becoming president constitute obstruction of justice.

History does not necessarily repeat itself, but sometimes it smells the same. And once again, Watergate provides a useful yardstick for measuring Trump’s Russia-gate. A review of how events unfolded over the two years of disclosures during the Watergate probe suggests a pattern: President Richard Nixon was involved in a cover-up to protect people close to him, not necessarily himself. It’s very possible that a similar story is unfolding today—that Trump’s undoing isn’t direct involvement in Kremlin-backed election interference, but rather obstrution of justice to protect both his son and his son-in-law for their role in the Russia scandal.

Let’s start with this simple fact: There is no evidence that Nixon knew about the Watergate break-in before it happened. All these years, tapes and congressional investigations later, nothing has emerged to prove that Nixon had advance knowledge of the Watergate operation against the Democrats that was being run by Gordon Liddy and E. Howard Hunt.

But Nixon’s good friend and former attorney general, John Mitchell, did have his fingerprints all over the Watergate operation, without question. The evidence is overwhelming that Mitchell, as the head of the Campaign to Re-Elect the President (known as “CREEP” to many) in 1972, approved the plans of Liddy and Hunt. And when Nixon found out about the break-in, he guessed as much.

It’s important to understand the nature of Nixon’s relationship with Mitchell to comprehend the president’s actions. The two were law partners in New York City after Nixon lost the governorship of California to Pat Brown, famously telling the press that he was done with politics. “You won’t have Nixon to kick around anymore,” he said, “because, gentlemen, this is my last press conference.” ...