May 16 (UPI) -- Since President Donald Trump excitedly announced that he would be accepting a $400 million plane from the Qatari government to serve as the next Air Force One, even members of his own party have expressed alarm.

There's the price tag of refurbishing the plane with top-secret systems -- upward of $1 billion, according to some estimates. Then, there are the conflicts of interest from accepting such a large present from a foreign nation -- what some say would be the most valuable gift ever given to the United States.

But it would also mark a striking departure from tradition.

While they're often variants of commercial planes, presidential planes have almost always been U.S. military aircraft, flown and maintained by the Air Force.

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