If the Yellowstone cauldron ever did blow, it would make Pompeii and Vesuvius look like a garden party.
It has, three times during the last 2.1 million years The caldera formed during the last of three supereruptions over the past 2.1 million years: the Huckleberry Ridge eruption 2.1 million years ago (which created the Island Park Caldera and the Huckleberry Ridge Tuff), the Mesa Falls eruption 1.3 million years ago (which created the Henry's Fork Caldera and the Mesa Falls Tuff) and the Lava Creek eruption 640,000 years ago (which created the Yellowstone Caldera and the Lava Creek Tuff), according to Wikipedia.
That was before my time, but you might ask Squantos about it. I wouldn't be surprised if he recalls it.
The geologists say that it's overdue.