If you ignore Japanese attacks on Alaska and Hawaii, which weren't states at the time, in World War II, this situation is new to America:
The U.S. “homeland is no longer a sanctuary,” according to the four-star general in charge of both U.S. Northern Command and North American Aerospace Defense Command.
Air Force Gen. Terrence O’Shaughnessy ended a speech at the 140th National Guard Association conference in New Orleans this weekend with a warning that the era of great power competition doesn’t leave the U.S. mainland uncontested.
Although the threat to the mainland is new.
This makes American forces have to face the threat our potential foes have long had of not having a rear area sanctuary. In the Cold War we would have hit peripheral Soviet bases, and today we'd do the same to Russia. And American strategy to overcome Chinese anti-ship weapons includes attacking the Chinese mainland-based military assets ("Bombing Beijing" is the term of art, I believe).
We will need to pay more attention to homeland defense. And National Guard units that aren't ready for deployment overseas will have a bigger role in attack recovery response much as they respond to natural disasters today.
Hopefully, the National Guard units established some years ago to respond to WMD attacks at home won't be needed for that role:
Recently, troops with the 46th Military Police Command of the Michigan National Guard began a three-year effort to respond to a chemical, biological, radiological or nuclear attack in Detroit. When they fill that role, soldiers in that unit fall under the command of the active Army, specifically U.S. Army North.
But it doesn't hurt to be ready for the worst.
