why did dallas county,AL go to gore by such a low margin?

[Terry the Fat Shark]

Assuming you are talking about Dallas County, Texas (which I'm not entirely sure you are based on the numbers in this post), Dallas County flipping is a rather recent phenomenon that happened by 2004, it has been growing steadily more blue ever since. It is fueled by a massive influx of population into Dallas County and the surrounding areas coupled with a broad shift in Texas politics that led to democrats growing in power across the urban areas of the State. Up until the 1990's, GOP did well in the urban areas and democrats did well in the rural areas because of how the parties were, but this flipped and so Austin (Travis county), San Antonio (bexar county), Houston (harris county), and Dallas (dallas county) all flipped or have been trending D (bexar and harris voted for abbott in 2014)