What if you have a new lease but old tenant won't move?

[Justin Donohue]

My wife posed this question to me and I wonder if anyone has ever had this experience? Say your current tenant is given notice to leave and you show your property in the meantime and find a new tenant to move in before they are gone. The date comes that the old tenant has to leave, but they don't. The new tenant is supposed to move in a few days or a week later. What do you do with the new tenant assuming they have already signed a lease?