The I-4 corridor is slowly trending Democratic. Western Pennsylvania is driving the republican shift.
It's not slowly trending Democratic, but moderately. Florida will always be competitive because of it's location in contrast to demographics. Many conservative immigrants move there as well. Look at Florida's distance from center for the past 60 years and you'll find it trended to the left but really hasn't varied alot recently. Pennsylvania may slide to the right of Florida, but Philadelphia will always keep it competitive even as it becomes center-right. So yes even in the next election, we may see a PA to the right of FL, but both states will be competitive and when Republicans win elections by more than a few points, Florida still may not be that competitive. I expect that for decades to come Florida will remain a leaning Republican state; purplish red.
