Sessions held the Senate seat from 1997 until 2017, when he was named President Donald Trumps first attorney general.
He was forced out of office last November after repeatedly clashing with Trump.
He was frequently mocked by Trump after he recused himself from special counsel Robert Muellers investigation into Russian meddling in the 2016 presidential election.
If he wins the Republican primary set for March 3, he will face Democrat Doug Jones, who won the 2017 special election to fill Sessions seat.
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