AHC/WI Best Possible Scenario for the Union

With any POD after June 8, 1861(the secession of TN), what is the best realistic scenario for the Union in the American Civil War, militarily speaking? How quickly and decisively can the Civil War be won by the US, assuming a war is going to happen against all 11 states of the CSA and US military and political leaders do everything right(or close to it)?
 
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