President Donald Trump’s confirmation Sunday that the United States may accept a presidential aircraft gifted from Qatar marked the latest escalation in his clash with Boeing, which is years behind on its government contract to build the new Air Force One.

Boeing has not officially confirmed any changes to the $3.9 billion fixed-price contract it signed during Trump’s first term. It has absorbed more than $2.5 billion in losses on the project.

Boeing has proposed delivering its delayed new version of Air Force One in 2027, a U.S. Air Force official said on Wednesday. President Donald Trump negotiated with Boeing for a pair of new 747-8 aircraft during his 2017-2021 first administration.