It was one of George W. Bush’s most viscerally powerful commercials against John Kerry in the 2004 presidential race: a pack of wolves lurking in a forest as a narrator accused Mr. Kerry of slashing intelligence gathering against terrorists. “Weakness attracts those who are waiting to do America harm,” the ad warned, as the wolves started running toward the camera.

Turns out the metaphor was subtle, at least by Donald J. Trump’s standards.

In his apocalyptic speech on Monday warning that terrorism could wipe out the United States — “There will be nothing, absolutely nothing, left,” he said — Mr. Trump substituted Muslim immigrants for the wolf pack. A single gunman carried out the Orlando massacre, he said. “Can you imagine what they’ll do in large groups, which we’re allowing now to come here?”

Exploitation of fear has been part of the American political playbook since colonial pamphleteers whipped their neighbors into a frenzy over British misrule. It took on new potency in the nuclear age with Lyndon Johnson’s “Daisy” ad against Barry Goldwater in 1964 and Jimmy Carter’s warnings about Ronald Reagan’s finger on the button in 1980.

But Mr. Trump — who drew harsh condemnation from President Obama on Tuesday — has intensified the power of fear in presidential politics by demonizing an entire religious group. And he has expanded the use of that power by stirring up fear in the aftermath of national traumas, like the San Bernardino, Calif., attack and now the Orlando shooting, that traditionally elicited measured and soothing responses from political leaders.