Violence, or at least the threat of it, has been a part of American political life from the beginning of the nation. Our third vice president, after all, shot and killed our first treasury secretary. Four of 46 presidents have been assassinated.

Last Saturday’s attempt to kill Donald Trump, former president and now Republican nominee, could be viewed as merely the most recent example. But it comes at a time when political passions are rising, guns are proliferating — and a significant political faction seems eager to invoke physical intimidation to advance its cause.

Members of the baby boom generation have seen this act before. In the period 1963-1981, the United States saw:

— The assassinations of President John F. Kennedy and Sen. Robert F. Kennedy.

— The killings of Black civil rights leaders Martin Luther King Jr. and Malcolm X.

— Segregationist presidential candidate and governor George Wallace paralyzed in an assassination attempt.

— Two attempts to kill President Gerald Ford that left him uninjured.

— The wounding of President Ronald Reagan.

That sorrowful list includes political leaders from the left and right and on both sides of the civil rights movement — and it understates the violent tone of American politics of the era, with segregationist killings in the south and left-wing groups that embraced violence.

The Reagan shooting in 1981 seems, in retrospect, to have been the last spasm of that bloody period. But under the precept that “everything old is new again,” Saturday’s shooting in Butler, Pennsylvania, is part of a renewed surge in political violence.

Some examples: The riotous “Unite the Right” white supremacist rally in Charlottesville, Virginia, in 2017. The conviction of nine men in a plot connected to a paramilitary militia to kidnap Michigan Gov. Gretchen Whitmer in 2020 (with five others acquitted).

And of course, the Jan. 6, 2021, Capitol insurrection. Widely condemned at the time, that riot is now shrugged off by leaders of the Republican Party. We note, for example, that on Tuesday at the Republican convention, Rep. Tom Emmer of Minnesota claimed that Trump stands with the police against “rioters” — a statement contradicted by the reality of Jan. 6, with Trump himself praising the rioters as “patriots.”

Violence is obviously damaging to our political system and culture. So is condemning one act of violence while excusing or ignoring another because it is aimed at a political opponent. Voters will do well to keep that in mind.

The attempted assassination of former President Donald Trump is part of a troubling surge in political violence.