Passengers use the self-check kiosks to get boarding passes for United Airlines flights at Denver International Airport, Saturday, Dec. 14, 2024, in Denver. (AP Photo/David Zalubowski)

Dressed in holiday garb, Leo, a 7-year-old Australian Shepherd/Heeler mix, greets passengers at Denver International Airport as part of the canine airport therapy squad Saturday, Dec. 14, 2024, in Denver. (AP Photo/David Zalubowski)

Travelers attach tags to their bags after checking in at the United Airlines counter at Denver International Airport, Saturday, Dec. 14, 2024, in Denver. (AP Photo/David Zalubowski)

FILE - Passengers line up at the security checkpoint in Pittsburgh International Airport Dec. 11, 2024. (AP Photo/Gene J. Puskar, File)