Anonymous, sorry I hadn't replied to your comment. An airborne tank would be in the same class as the M8 Buford or an M-113 ACAV. It has been the shortfall of the airborne/light units in the US Army.
However, on further reflection, the true Army capability shortfall is in field artillery. There are two components to this short fall: human and materiel.
[SHORAD has been drastically cut back as well, but there wasn't much to start with in the first place. If the USAF cannot come through on the air superiority piece, we'll be in for a tough, long fight.]
Human: The wars in Iraq and Afghanistan has depended heavily on artillerymen serving as Dragoons (mounted infantry). In the process artillery collective training has fallen by the wayside. In the chaotic dwell time back at home, there is too much turnover to get any benefit out of collective training. Much of the training focus is on the war time mission of convoy security and dismounted operations. A few of the batteries get lucky and draw an artillery fire support mission during deployment. These lucky batteries get to train on the artillery collective tasks, but there is little institutional memory instilled, because of the personnel turnover later on and because they probably won't do artillery fire support the next deployment.
So it is a real question if anyone will remember how to shoot a Table VIII to the standard by the time we get out of OIF/OEF. [Table VIII is the 8th table in the 12 gunnery tables of the collective training pyramid, 12 being a fully proficient battery. 8 means proficiency at the section level: gun lines, FDCs. During the Cold War, few units got past Table VIII, and never in a repeatable, year to year, manner.]
If people don't know how to shoot a Table VIII, then we will start shooting our own people by mistake. Of course, the situation is fixable if we bring back all the retired red legs as contract consultants and rebuild our field artillery branch. But it will take a long time, and during that time the US Army will have a gap in its conventional capabilities.
Materiel: On the materiel side, we have a gap in fire delivery. The acqusition trend is going toward precision munitions and away from dumb weapons like regular shells and DPICM rockets. So we will be short on stock for sustained volume fire, should we ever need it again. In addition, the Assault Breaker project was essentially abandoned. So the US Army is short in the Deep Fight arena. Granted, we will have plenty of smart weapons to take out the high valued targets, and Apaches will still swarm with their Hellfire volleys. But the OMG over the Fulda Gap? Not so much anymore.