It wasn't just Chevy Chase. Every chance the media got they got they blinded Pres. Ford with the Kleig? lights and then he'd (understandably) end up tripping over some cable taped to the floor, threshhold, hatch opening, etc.
There were probably months of footage of him not stumbling or tripping or bumping his head on the cutting room floor.
(Future President ) Gerald Ford, Second from right front row...
Note Catapults
USS Monterey