Fog alerts lead to ripple effect of flight delays nationwide, slowing Christmas Eve travel rush; New video of extensive Hamas tunnel system released by Israeli military; Respiratory illnesses on the rise across U.S. as millions gather for holiday weekend; and more on tonight's broadcast.

U.S. conducts airstrikes against Iranian-backed militias in retaliation for attack on Erbil Air Base; Israel warns war with Hamas will go on for many more months; Thousands of migrants join caravan in Central America headed for U.S.; and more on tonight's broadcast.