An assembly for a vehicle includes a front pillar and a rear pillar. The front pillar and the rear pillar define a door opening. The vehicle includes a first track supported by the front pillar and a second track supported by the rear pillar. The vehicle includes a bar extending from the first track to the second track. The bar is moveable relative to the first track and the second track from a lowered position to a raised position. The bar extends across the door opening in the raised position. The vehicle includes an airbag supported by the bar. The airbag is inflatable to an inflated position when the bar is in the raised position.