Does Donald Trump only believe stuff he gets from right-wing email chains?

It's starting to seem like it.

A terrorist drove a van down a busy pedestrian street in Barcelona, Spain yesterday, killing at least 13 people and injuring as many as 80.

Donald Trump has responded to this tragedy by resurrecting a fake news story from the campaign trail about how a US General stopped terrorism in the Philippines by shooting captured Muslim insurgents with bullets dipped in pig's blood.

"Study what General Pershing of the United States did to terrorists", Trump tweeted, "There was no more Radical Islamic Terror for 35 years!"

This Pershing story is literally fake news. It never happened.

Politifact gave it a "pants on fire" lie rating when Trump first mentioned it at a South Carolina campaign stop last year.

So why is the president still talking about it, especially at a moment like this?