What changed from 1996 to 2004 between Alabama and Mississippi?

[WalterWhite]

From 1972 to 1992, Alabama always voted to the left of Mississippi. That trend was broken in 1996 when Mississippi voted to the left of Alabama. Things reversed themselves in 2000, when Alabama again voted to the left of Mississippi.

Since 2004, however, Alabama has voted to the right of Mississippi in every presidential election. What changed between 1996 and 2004 for that to happen?

[OSR stands with Israel]

African American Turnout Started to go up in the 1990s

[TDAS04]

Republicans maximized the white vote in Mississippi earlier than in less black Alabama, and there continued to be a sizable share of conservative, yellow dog Democrats in northern Alabama through about 2002.

[Vice President Christian Man]

Whites in the Northern part of the state started rapidly moving towards the GOP starting in 2004 turning it from a reliable "R" state to a solid "R" state. Mississippi mostly lacked that population except for in the NE corner and along with its strong AA population made it more competitive at least compared to Alabama, although staunch partisanism will prevent a Dem from winning unless we see either a Roy Moore type of situation or demographic changes occur. 

[Mr.Phips]

Whites in the Northern part of the state started rapidly moving towards the GOP starting in 2004 turning it from a reliable "R" state to a solid "R" state. Mississippi mostly lacked that population except for in the NE corner and along with its strong AA population made it more competitive at least compared to Alabama, although staunch partisanism will prevent a Dem from winning unless we see either a Roy Moore type of situation or demographic changes occur. 

Yeah, even in losing races Democrats often still carried the northern 1st House district.  In 1988, when Trent Lott was winning 54%-46% statewide in the senate race, he still lost the 1st district.