The arc of partisanship in impeachment, to some extent, matches the increased polarization of politics in America over the last 45 years. It moves from consensus to deadlock.

When the House Judiciary Committee votes on articles of impeachment against President Trump, the vote is expected to be along purely partisan lines — a far cry from the committee impeachment vote against President Richard Nixon in 1974, and different too from the President Bill Clinton's impeachment in 1998.

Back in 1972, it wasn't the break-in at the Democratic headquarters that triggered the Nixon impeachment inquiry. It wasn't even the Senate Watergate Committee hearings that riveted the nation a year later. It was the Saturday Night Massacre, when President Nixon fired special prosecutor Archibald Cox and shut down his investigation.

"Constitutional Crisis"

"The country tonight is in the midst of what may be the most serious constitutional crisis in its history," intoned NBC's John Chancellor on the Nightly News after the attorney general resigned rather than carry out the firing order and the deputy refused, only to be fired. Ultimately, Solicitor General Robert Bork would carry out Nixon's orders. But it was all for naught.