Project Sundial wasn't just theoretical. We had the ability, the materials, and the technical knowledge to build it. The political will faltered and blinked.

You know how you can absolutely verify that? We built it in thousands of different bombs rather than just one big one.

If we had made a 10 gigaton device where it was supposed to be located in eastern California, or western Nevada, blowing that up would have created a massive crater that probably would have measured at least 30 miles in diameter, and all of the US would die in the first blast. Normally when talking about nuclear or fusion weapons I would call the US citizens the lucky ones, because we wouldn't have to live with the consequences. In this case, all of humanity is lucky, and basically no one survives the blast shockwave. The shockwave would circle the globe multiple dozens of times. No one that isn't in a fortified bunker will survive the 1000 mph winds that would cause. Those winds would sandblast the surface almost smooth.

This is a world ending bomb. Half the planet's crust would be molten for decades if not centuries. It would probably be the first mass extinction event that kills off more than 99.9% of all species. 10 gigatons is about 1/4-1/5 the amount of energy that Theia imparted to Proto-Earth which created two moons for a very short period of time, and made the entire planet molten for another 1/4 billion years.

Oh, and I agree with Teller on this one. He, correctly in my view, assumed that the end game of fusion weapons was a way to end all life on Earth, and designed the endgame. I think we were very stupid to split that up into massive stockpiles that, "maybe we could use one or a few, but not all of them." That's far too big of a risk for normal humans. Someone will use them again if they are as small as they are.