Past impeachments, products of their times, often produced unintended consequences

Impeachment of the president has reared its head five times in American history, and all five episodes should serve as cautionary tales for those House Republicans who now seem determined to make it six.

Each of these earlier forays had a profound impact on the direction of national politics, both in the short term and for years to come.

Four of the five reached the point of impeachment votes in the House and trials in the Senate that failed to muster the two-thirds vote required to convict.

The one process that did not go the distance ended just before the House took its vote. It stopped because the target president, Richard M. Nixon, had resigned and left town. That was the only impeachment process that actually drove a president from office, and arguably the only one that clearly succeeded in what it set out to do.

It is not yet clear that the "impeachment inquiry" announced last week by Speaker Kevin McCarthy will even lead to formal charges or a vote in the House. But McCarthy said several House committees would get to work