How many elections does it take for a swing state to become a political party dominate state?

Example, Michigan is a swing state, and has voted democratic for the past two (maybe three... don't quote me) elections. My question is how many elections have to occur, with the same vote, before it becomes a dominant democratic, republican, etc. state?|||The people also factor into that equation. Michigan has a substantial black population that will almost always vote democrat. Along with all the factory workers who traditionally vote democrat. Then you have Texas with a very large christian population who vote republican. Nevada is a good example. In most Presidential elections since becoming a state, Nevada has gone republican. Most of the rural NV counties are conservative, so they vote republican. But Washoe and Clark Counties(Reno and Las Vegas) have a substantial liberal population and have an population out numbering the rest of the state. So NV can become a swing state because of the ratio of conservative to liberal.