Cancel government order for a new Air Force One.

The Air Force said previously that it had earmarked $1.65 billion for two new presidential aircraft, which will be four-engine Boeing 747-8s. The source of Trump's $4 billion cost estimate for the program was not immediately clear, although a Government Accountability Office report from last March priced it at roughly $3.2 billion.

The Pentagon announced the deal with Boeing last January, awarding an initial contract worth nearly $26 million for initial research for the new planes, according to Reuters. The Defense Department awarded an additional $127.3 million contract in July to develop interior, power and electronic specifications for the next-generation aircraft, according to FlightGlobal, a publication that covers the aviation industry. "We are currently under contract for $170 million to help determine the capabilities of these complex military aircraft that serve the unique requirements of the President of the United States," Boeing said in a statement released Tuesday morning. "We look forward to working with the U.S. Air Force on subsequent phases of the program allowing us to deliver the best planes for the president at the best value for the American taxpay