Also , it will also be just a regular plane, not hardened and beefed up like other Air Force One jets. They're typically better shielded against gunfire, missiles, etc. Able to jink sideways/up/down to dodge enemy fire. To eject chaff to confuse enemy rader. To be re-fueled in-flight so they can serve as a safe command center for days, weeks, months. Etc.
Retrofitting an existing plane to do all of that may cost MORE than just building it that way to start. Current estimates are over $1 BILLION. So, Trump gets to brag about the plane "given" to him by his "admiring fans" in Qatar, gets the US taxpayers to pay a fortune to beef it up, and gets to take it with him when he leaves office. In what world does that sound like a good idea? How stupid are WE?!?!?