This kind of abuse is not just restricted to High level officials. It permeates the entire Government Structure. And it all came about from a "Cost Saving" measure introduced to Government Employees (Including Military) about 15 years ago.
Back in the day, when someone went on required Government Travel, they would have to submit a request to the Agency Comptroller who would issue GTR (Government Travel Requests), based on formulas established by the JTR (Joint Travel Regulations). They would also give advanced per diem in cash to the traveler, and make necessary reservations for travel and hotel. The GTR would be exchanged at the carrier for airline, bus, train, etc. tickets. When the travel was completed, the traveler would file a travel claim which, when processed, would allow the traveler to be reimbursed for shortages or their pay debited for overages.
Of course, there was a tremendous amount of time and paperwork involved in this process, so the Government came up with the Government Travel Cards. Basically a Visa or Mastercard issued by the Government in the employee's name. The employee would make all travel and lodging arrangements, and put it on the card. When travel is completed, the employee completes the travel claim and is reimbursed for the costs. The bill goes to the employee, who pays it when they're reimbursed. (High up officials have cards that bill straight to the Govt)
Where the breakdown is, is when the employee books that first class flight or 5 star hotel. If it's put on the travel claim, the government pays it. The employee may be counseled to use less expensive methods in the future, but the Govt still pays it. Essentially there is no oversight until after the fact, and employees aren't disciplined if they misuse the card. The worst thing they do is take the card away.
The problem in the Military is many members use it as a personal card and charge non-official stuff to it. Sporting goods, tires, car repairs, gifts for spouses, vacations, etc. Hell, even strip club tabs have been charged to Govt Cards. The Govt doesn't know what's going on the bill, because it goes to the member, and they aren't notified until it goes 90 days delinquent. They CAN punish under the UCMJ, and dock pay until it's paid off.
But if the Service Member gets out without paying the bill, the Govt is stuck with it, and doesn't prosecute because the member is usually no longer subject to the UCMJ. In one year the Navy had several million dollars in unauthorized charges that they were stuck with.
I think they've tightened up on the cards, but they're still getting nailed to the tune of a few hundred thousand a year.