Anonymous wrote:USNA grad here.
1 -- Inter-service transfers (after graduation, before commissioning) do occur, mostly a legacy of when there was no Air Force Academy. But they are very rare, 10-15 per year per school (usually "graduation physical" related; one service would let you fly where the other would not, or someone who could no longer fly...).
2 -- There is a well-established exchange program (spend a year at the other school); that's another 10-12 people/year. Depends on your major (hard for some types of engineers to do it, as you have to be able to keep up with your studies while you are gone) and it is very competitive.
3 -- You can theoretically leave USMA during your first two years and apply for entry to USNA just as you could from any other college (I had a friend who spent two years at Citadel and then applied to USNA). You cannot leave after the start of your junior year, though. Many midshipmen went someone else first for a year or two. Classes you have completed that Navy offers could be credited to your record so you could take advanced ones. But you still have to spend four years there to graduate (be a plebe TWICE?), and I am guessing few of the USMA plebe credits other than basic freshman classes would transfer (just as Naval Science 101 wouldn't transfer anywhere).
4 -- Now, would a congressman balk at spending two slots on one person? Depends on where they are; there are places in the US where there is not that much competition for a slot and so the congressman has ceded the whole discussion over who gets the slot to the Academy admissions office ("pick who you want and I'll sign the form"). They might not care much. The DC area, though is not one of those; it is VERY competitive here because there are so many alumni children who both attend really good schools here and know of the opportunity.
This, 100%. And one additional commissioning source is pre-arranged specialty-line commissioning. You graduate from the USMA, for example, and are immediately commission in the USAF. This happens perhaps a half dozen times per year, in each case by prior approval of the two Superintendents involved.