Mark Zuckerberg is facing a backlash from within Facebook after several senior employees publicly criticized the chief executive for refusing to take action over posts by President Donald Trump that Twitter censured last week for “glorifying violence.”

As protests and rioting over the death in police custody of George Floyd, an unarmed black man, spread through several American cities this weekend, Mr. Zuckerberg was forced to defend Facebook’s position as—in his words—“an institution committed to free expression.”

On Friday, Mr. Trump posted on both Facebook and Twitter that he would respond to violent protests with military force, saying: “When the looting starts, the shooting starts.” But while Twitter slapped a warning on the post and hid it from view, Facebook left the message intact.