Serving overseas, I have seen numerous official delegation trips that were supported by VIP Aircraft and an extensive DOD team. For example, a five-member congressional delegation traveling overseas will be supported by a business jet, flown by two Air Force pilots. They will be accompanied by at least two military officers and one or more enlisted personnel- not to mention additional support from the State and DOD personnel already stationed overseas.
Setting aside the human cost of this travel, the aircraft itself imposes significant costs. One trans-atlantic flight will burn tens of thousands of dollars in jet fuel and incur charges for parking at the foreign airport; not to mention the tens of millions of dollars which are spent to procure the jet initially and the hundreds of thousands of dollars to annually maintain it.
While I firmly support travel by Congressmen, Senators, and senior administration officials overseas, I also believe that some of the trips simply would not take place if they were not supported by the military with business jets. If exigencies of the public business require a dedicated business jet for travel, it would be significantly cheaper to rent planes and pilots on an as-needed basis, rather than maintaining them in-house.
Limiting use of the military VIP aircraft fleet to only a handful of U.S. officials with extensive foreign travel requirements and special security arrangements (i.e. the President, Vice President, Secretary of State, and Secretary of Defense) would not only save hundreds of millions of dollars annually, it would produce an immediate windfall if the no-longer-needed aircraft could be sold. Not only that, but flying commercial (even business-class commercial) would result in lower greenhouse gas emissions (per-seat emissions are lower on commercial aircraft) and significant annual savings- both in forgone trips and in much lower costs for those trips which really are in the public-interest.