The US has an area of 9.857 million km²
The earth has an area of 510.1 million km²
So the earth would suddenly lose a little under 2% of it's mass.
Suddenly there's something like 20 billion cubic km of vacuum where liquid rock and rock used to be.
This is unfortunate since the earth may not have enough air to fill the hole.
A storm the like of which the world has never seen with winds at the speed of sound tears in the direction of the hole. Water flood in around the edges but not nearly so fast.
Anyone near the border is dead immediately as winds tear buildings and sections of city into the hole.
but that's ok, those people were going to die soon even if the hole wasn't a vacuum.
The earths atmosphere around the hole basically falls into the hole. A front spreads at the speed of sound from the hole.
The material of the core and mantle would collapse into the vacant space, the energy of the sudden violent movement would heat it up to an even higher temperature than it currently is.
The hole would be far too big to hold itself open against gravity; On that scale, the rock in the crust would behave more like a liquid. In the space of about half an hour, the hole would undergo a slow-motion collapse.
As they collapsed, the rocks around the hole would heat to a glow. At the center of the hole, a white-hot jet of rock would fountain outward into space.
Some of this would shoot off into space, some would end up in orbit and megatons of white hot lava would simply rain down across the earth.
Earthquakes would crack the crust like an egg across much of the planet as shockwaves rippled out. Tsunamis would tear across the atlantic and pacific and wipe out most of the cities along either coast.
Even the indian ocean probably wouldn't be spared since shockwaves would likely focus together at the exact opposite side of the world to the US as well causing the crust at that location to tear open.
Over the following hours and days volcanos would burst to life or form anew across much of the planet as the earths crust shifted.
megatons of air and water flooding into the hole is causing explosions and ejections of material larger than the largest megavolcano.
The sky is filled with ash and poison. The sun is blotted out.
Ocean levels drop globally as water continues to drain into the massive hole.
The water flash boils blowing gigatons of material into the atmosphere.
Earthquakes on a scale never seen before continue to turn cities to rubble everywhere. The tectonic plates themselves likely crack.
Humanity has little chance of surviving this.