Oh dear, I agree with @gailcalled and @chyna then @rooeytoo in great measure! Yes, the water is being heated, so steam escaping reduces the water content, but as you heat the meat, the proteins are also being ‘hear-shocked’ repeatedly. This shortens the protein chains… Sorry to get technical, but you did ask! It makes the meat tougher each time it is heated.
BUT: each time you have ‘leftovers’, the bacteria that are naturally around in the food and the air get a chance to grow. So as @rooeytoo says, you must only heat what you need to eat at the time. Do NOT keep re-heating the same food in total, all kinds of nasties may be breeding in it and you may eventually get sick. Not to mention that each episode of heating destroys vitamin content. Keep the food at a constant cool temperature until you need some, then ONLY heat what you need. Or invite some friends over and have a party. Just don’t keep doing that stuff with this Turkey! :O(