0-25% solid Dem
15% soft Dem
15% soft Rep
25% Solid Rep
The "base" for both parties is between 25-40%. If their approval falls below 40% they are losing their base. If it's above 50% they have their base and the majority of the Independents. Above 60% and they have all that and some from the other side. Even in war it is unlikely to get above 75%. The total voting will be something around 100 million.
After all is said and done the election will come down to a few percentage points around 50%.
Let's look at Independents. Assume that both sides have their base, which they will by November, barring a third party run from either direction. Both sides will be working on getting the majority of the 20% of independents. If one side has 51% total then what that really means is they have 11% of the 20% independents or a percentage of 55% to the others 45% of independents. Think about that. Having 51% is a much bigger deal than it first appears. To make that even they would need to change 5 million votes!
Another thing. Remember that old term, little used lately, "The loyal opposition"
It is the duty of the opposition to represent the people who voted for them and opposing what the other side does is the right and proper thing for them to do. Somehow that gets lost in all the yelling and screaming heard today.