Donald Trump promised to work for repeal of the Johnson Amendment the day he learned about it last year during a meeting with Christian evangelical leaders who had been slow to express support for his campaign. President Trump repeated that promise at last week’s National Prayer Breakfast, characterizing the amendment as a limit on religious freedom. The amendment restricts religious groups’ direct involvement in politics — but in doing so it protects both religion and the government.

The Johnson Amendment, sponsored by then-Sen. Lyndon Johnson and signed into law by President Eisenhower in 1954, is a provision of tax law that forbids 501(c)(3) organizations from engaging in partisan political campaigns. Such organizations include most charities, universities and, most notably, churches, temples and mosques. Violators of the amendment may lose their tax-exempt status, and their donors may be barred from making tax-exempt donations.

The amendment is lightly enforced. Despite a rising tide of political activism among religious groups, only one church has been investigated for partisan advocacy and none has been punished. Yet the amendment is widely observed all the same — perhaps because most religious leaders understand that it benefits them more than anyone.

The surface rationale…