The Trump administration plans to accept a luxury Boeing 747-8 plane as a donation from the Qatari royal family that will be upgraded to serve as Air Force One, which would make it one of the biggest foreign gifts ever received by the U.S. government, several American officials with knowledge of the matter said.

The plane would then be donated to President Trump’s presidential library when he leaves office, two senior officials said. Such a gift raises the possibility that Mr. Trump would have use of the plane even after his presidency ends.

Mr. Trump confirmed the fact that he anticipates receiving the plane in a post on social media on Sunday evening, after a day of controversy in which even some Republicans privately questioned the wisdom of the plan. Mr. Trump suggested that Democrats were “losers” for questioning the ethics of the move.

“So the fact that the Defense Department is getting a GIFT, FREE OF CHARGE, of a 747 aircraft to replace the 40 year old Air Force One, temporarily, in a very public and transparent transaction, so bothers the Crooked Democrats that they insist we pay, TOP DOLLAR, for the plane,” Mr. Trump wrote. “Anybody can do that! The Dems are World Class Losers!!!”

While a Qatari official described the proposal as still under discussion and the White House said that gifts it accepted would be done in full compliance with the law, Democratic lawmakers and good government groups expressed outrage over the substantial ethical issues the plan presented. They cited the intersection of Mr. Trump’s official duties with his business interests in the Middle East, the immense value of the lavishly appointed plane and the assumption that Mr. Trump would have use of it after leaving office. Sold new, a commercial Boeing 747-8 costs in the range of $400 million.

“Even in a presidency defined by grift, this move is shocking,” said Robert Weissman, a co-president of Public Citizen, a consumer advocacy organization. “It makes clear that U.S. foreign policy under Donald Trump is up for sale.”

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