At two of the nation’s most historic black churches, sermons reflect on Martin Luther King and take sharp aim at Trump

The Rev. Raphael G. Warnock had not planned to mention the words “Donald Trump.”

It was the day before the Rev. Martin Luther King Jr.’s birthday, and Warnock was going to focus elsewhere.

But after the president was said to call African countries, El Salvador and Haiti “shithole” places last week,...