No two scandals are exactly alike. Nor are any two elections, or any two impeachment efforts.
But as long as President Donald Trump's self-inflicted injuries are so widely compared with Watergate, it might be a good moment to hear the echoes of another past president's run-in with the Constitution.
Democratic leaders in Congress did not try to remove President Ronald Reagan, who was in his second term when word broke of what became known as the Iran-Contra scandals.
For one thing Reagan was popular. For another, his own aides spoke of working to give him "plausible deniability" regarding White House transgressions. In the 1980s, the run-up to President Richard Nixon's resignation in 1974 still was in the rearview mirror at the Capitol.
But some facets of Iran-Contra sound new again.
Members of Reagan's inner circle used private and foreign players for purposes unsupported or clearly opposed by Congress. Even some administration insiders advised against the approach.
Weapons were involved. Delivering them was supposed to get the Reagan administration a dearly desired result, as appears to be the case with Trump in Ukraine.
From there the stories diverge. American TOW missiles were circuitously approved for sale to Iran, despite U.S. sanctions, so Tehran would free U.S. hostages. Some related funds were earmarked to go to the Contras rebelling against Nicaragua's Sandinista government.
Both houses of Congress got laws enacted to stop Reagan's funding for the Contras, so private backdoor means were sought. The president told subordinates he wanted the guerrillas held together "body and soul."
By the time his State of the Union Address in January 1987, Reagan conceded, "We did not achieve what we wished, and serious mistakes were made in trying to do so. We will get to the bottom of this, and I will take whatever action is called for."
Later, National Security Council staffer Oliver North was found to have altered and destroyed records about his efforts to raise money and arms for Contra fighters. He was convicted on three charges that were later vacated. National Security Advisor Robert MacFarlane got two years' probation on a guilty plea of withholding information from Congress and National Security Advisor John Poindexter was convicted of false statements, but his case was vacated by an appeals court.
Under Reagan's successor, Republican George H.W. Bush, Trump's Attorney General William Barr — then as now running the Justice Department — worked on grants of clemency for ex-Reagan officials, including former Defense Secretary Caspar Weinberger. Weinberger had been scheduled for trial for allegedly lying to Congress.
By the early 1990s, Sen. Daniel Patrick Moynihan (D-N.Y.) was calling the Iran-Contra affairs "the most ominous constitutional crisis in modern American history." Moynihan, who is deceased, warned that, "the most extreme doctrines of presidential immunity in foreign affairs are asserted with ever greater confidence and with no rebuttal."
In the current scenario Trump delayed legal, bipartisan-backed missile sales to Ukraine, while also trying to get that nation to investigate Americans who happened to be his political detractors.
So the Reagan administration appeared to exceed its constitutional authority in order to leverage the release of captive Americans and fight communism in Latin America.
But at the moment it appears Trump operated his shadow foreign policy through private lawyer Rudy Giuliani in order to muddy up an election opponent even if the president also tries to sell it as an unlikely effort to fight corruption in another country.