The air force is unique in that it has major responsibilities that could (some say should) belong to the other services. For example, many armies have their own ground support warplanes. But the USAF demanded control of everything that flew, and got it's way in the 1950s (except for naval aviation and helicopters). Ever since, the army has bitterly complained that the air force was ignoring the army's needs. No matter, the air force controlled the aircraft and, while on paper there was plenty of ground attack and transport planes, in reality the army was pretty much on its own. Same situation with air transports. Again, the air force demanded that it have control, so now the army and navy have to dance to the air force's tune when it comes to getting things overseas in a hurry. Similar situation with aerial tankers, logistics and many other obscure, but expensive military items. The air force takes money intended for what it says it is doing, or should be doing, and constantly builds new aircraft. It's a "too much ain't enough" philosophy run amok.
And it's nothing new. Between 1939 and 1952, there were fifteen different heavy bombers developed. Two were cancelled. The rest went into production. By the 1980s, there were four heavy bomber types in service. Even though the ICBM came into service during the 1960s, and was acknowledged as a superior method of delivering nuclear weapons, the air force spent more on bombers than on ICBMs.
Why? Because pilots run the air force. Until the 1980s, bomber pilots tended to be the big shots. This was a legacy of World War II, where bombers were the most impressive, if not the most effective, example of air power. For two decades after World War II, the bomber pilots controlled the only means of delivering nuclear weapons. Things changed when the modern fighter-bomber (like the F-4 Phantom) arrived in the early 1960s. Vietnam gave a generation of fighter pilots so much combat experience that the bomber generals were replaced by fighter jocks in the 1990s. The bomber generals still have a lot of clout, and the air force is still a big believer in the B-2, even though it is very expensive to maintain (and can only operate from U.S. bases because of that.) The air force wants to build more B-2s (Congress stopped production at twenty airplanes) and there is talk of how wonderful it would be to have a B-3.
The latest showdown is over the establishment of a "Space Force" to deal with the increasing activity beyond the atmosphere. In addition to a growing number of satellites, there are plans to put up space "battle stations" as part of an anti-ICBM program. Functions currently carried out by AWACs, J-Stars and electronic warfare aircraft are to be transferred to larger, more capable, and more expensive, satellites. The air force wants to own the Space Force. The army and navy want the Space Force to be a separate service. The Space Force will require hundreds of billions of dollars for satellites, sub orbital (flying at the outer limits of the atmosphere) spacecraft and space stations. The soldiers and sailors fear that, once the air force gets it's hands on all that Space Force loot, a lot of the money will end up in new fighters and bombers. While setting up a new military bureaucracy is not popular, building extraordinarily expensive warplanes is even more unpalatable.
Too Much Ain't Enough; The US Air Force is under attack for being too successful. We're not talking about bombing and dogfights, although the air force is very good at that. No, this is about what really drives the military in peacetime; money. The air force is grabbing ever larger chunks of the budget and spending it on things the army and navy consider unnecessary. In wartime, you keep score with battles won and lost. Same thing in peace time, except that you use paper bullets and the battles are over trillions of budget dollars For the last fifty years, the air force has been the consistent winner. That, in itself, is not the problem. What the air force does with it's winnings is. The two billion dollar (each) B-2 bomber and two hundred million dollar (each) F-22 fighter made it clear that, whatever else the air force was supposed to do with all their money, most of it was going into building increasingly expensive aircraft. Not that the army and navy are pristine in this respect. The navy used budget sleight of hand to build a new fighter (the F-18D, which was a new aircraft in all but name.) The army is building combat helicopters that cost as much as some jet warplanes. But the air force is in a class by itself, which is why it's in everyone's crosshairs.