Mitt Romney is hoping for a breakout victory in primary votes in America’s conservative deep South, looking for a win in Alabama or Mississippi that would accelerate his campaign for the Republican nomination.
The former Massachusetts governor holds a commanding lead in delegates to the national convention in Tampa, Florida, in August.
He is facing, however, tough challenges in the two southern states from rivals Rick Santorum and Newt Gingrich, who were battling it out to emerge as the sole conservative challenger to more moderate Mr Romney, a patrician multi-millionaire who amassed his fortune as a venture capitalist.
The conservative base of Republican voters nationwide has been slow to embrace Mr Romney, distrusting him over moderate stands in the past on social issues like abortion and gay marriage.
Slower still to fall in behind him have been voters in the South, where he has yet to win a primary.
The showdown vote occurs as new polling showed a steep drop in Barack Obama’s approval ratings, a decline that coincides with rapidly climbing petrol prices as a result of renewed turbulence in the Middle East.
A Washington Post-ABC News poll found that 46% of those surveyed approve the way the president is handling his job, and 50% disapprove. A New York Times/CBS poll found 41% approval, and 47% disapproval.
A win in either Mississippi or Alabama would be an important breakthrough for Mr Romney, easing concerns that the Harvard-educated North-easterner cannot win the party’s most conservative and evangelical Christian voters.
Mr Gingrich, the former speaker of the House of Representatives, is banking on a strong showing to keep his candidacy alive.
Mr Santorum, a former Pennsylvania senator, is labouring to prove his claim that Mr Romney – who is way ahead in the delegate count – cannot secure the support of the powerful conservative bloc in the Republican base.