In some states you can without special license in others you must have a commercial doubles license and in most it is illeagal. You will have to know the laws where you will be driving. I know in Oregon its leagle to tow doubles as long as you don't go over a certain length.
Don't come through Virginia or surrounding states. I also agree with John on the strength of the bumper. Trailer frames, not just at rear, are NOT designed to tow something behind. I know it is done, but they just aren't designed for it.