Missouri is among those battleground states, but you miss the point. Amending the Constitution requires a 2/3 majority of the states to ratify -- and you can't get 2/3s to do that because it means taking a lot of electoral power away from Arizona, Alabama, Kansas New Mexico, Missouri Montana, Ohio, Wisconsin, Minnesota, Wyoming, the Dakotas, Kentucky, Idaho, Mississippi, Utah, Nebraska, Tennessee, and Texas -- and a half dozen others I'm skipping from memory. Too many states would oppose the idea.