Probably switched to a 757 as they are quite a bit cheaper to fly than the 747. But, then what does he do for communications, etc? I know Boeing outfitted two (maybe three?) 747s to serve as Air Force One aircraft, but I don't they did any 757s to the same level. There are 757s in the government/Air Force stable, but I didn't think they were outfitted to be Air Force One command post aircraft......
I couldn't get any details from the Andrews AFB base site (wouldn't download). But I did find reference on the 'Net to "Air Force Two," a Boeing 757. Makes sense for domestic travel. I guess I never really thought about it before - just always had that 747 vision in my head.