Depends. I tend to define a swing state as a place with regular changes in the state legislature, regular shifts in Senate and Presidential elections, and registration more or less evenly divided. Missouri and Florida are currently "swing states" by my definition. My home state of New York, which has a long history of alternating between RINO and Dem-Socialist governors, cannot be considered a swing state because 1. Margins of victory for Dem politicians are usually considerable. 2. Dems outnumber Republicans by a wide margin and 3. the only Pubbies who get elected in New York are those who govern like Democrats.
New York State Politics in a Nutshell: Republicans = Democrats, Democrats = Socialists.