Looks like our air defenses are about as good, or as bad, as the Soviets used to have. Back some years ago a German teenager flew a Cessna all the way into Russia and landed it in Red Square, right in front of the Kremlin. The Russians freaked, this was back in the cold war, and they figured if a German kid could make it thru, SAC could as well. Some Russian heads were rolled over the affair.
Yesterday we had a guy land a Gyrocopter (very small one man autogyro) right on the Capitol lawn. He flew it down from Gettysburg PA. He probably never exceeded a couple of hundred feet altitude, and the radar cross section of a little, largely wood, autogyro is SMALL. The radar never saw him, and even if it had, he would have looked like any other light plane. The restricted airspace around DC ain't that big, and it was probably only minutes from the time he crossed into the DC no-fly zone and he landed at the Capitol.
So, if it can happen to the old Soviet Union, it can happen to us. The Gyrocopter is too small to carry much in the way of munitions. You could do more damage ramming an SUV thru the Capitol gates. It's given us a lot of amusing TV news. I hope the guy that did it gets off with a scolding.