WASHINGTON — When President Trump told an audience of religious leaders on Thursday that he would ‘destroy’ the Johnson Amendment, he declared his intention to sign a bill that would fundamentally alter a major aspect of the church-state divide that has been a constant in American politics for generations.

But what exactly is the Johnson Amendment?

A restriction for churches and nonprofits

It is one of the brightest lines in the legal separation between religion and politics. Under the provision, which was made in 1954, tax-exempt entities like churches and charitable organizations are unable to directly or indirectly participate in any political campaign on behalf of, or in opposition to, any candidate. Specifically, ministers are restricted from endorsing or opposing candidates from the pulpit. If they do, they risk losing their tax-exempt status.

Considered uncontroversial at the time, it was passed by a Republican Congress and signed into law by President Dwight D. Eisenhower, a Republican. Today, however, many Republicans want to repeal it.

The ‘Johnson’ is Lyndon Johnson

Back when Lyndon B. Johnson was a senator from Texas, he introduced the measure as an amendment to the tax code in 1954. Like many things Johnson did, the goal was to bludgeon a political opponent, in this case a rival in a primary who had the backing of nonprofit groups that were campaigning against him by suggesting he was a communist. Though there was no church involved, according to PolitiFact, churches were covered by the bill as well.