Candidates vying for the U.S. Republican presidential nomination are making their final push for support in South Carolina just one day before the southern state holds its primary.

The four candidates are meeting with voters across the state on Friday, each aiming to show he is the one who can defeat President Barack Obama in the national election in November.

A week ago, many political polls indicated the South Carolina race would be an easy victory for former Massachusetts Governor Mitt Romney. But after sharp attacks from his rivals, and a series of upheavals in the race this week, many polls and political analysts say the race could be much closer.

Former congressman Newt Gingrich, in particular, is rising as a challenger to Romney. He could benefit from Texas Governor Rick Perry's decision to drop out of the race Thursday, and to endorse Gingrich.

Romney joined Gingrich, former Pennsylvania senator Rick Santorum and Texas Congressman Ron Paul in a volatile debate in South Carolina Thursday night.

The final four contenders argued over jobs, health care, and leadership. Gingrich turned angry when questioned at the start of the debate about allegations by his ex-wife that he asked for an “open marriage” in 1999 to accommodate an extramarital affair. He denied that accusation, although the former speaker of the House of Representatives has admitted having affairs during his first two marriages.

For many American voters, the U.S. economy and high unemployment are the big issues in this election. President Obama has no competition for the Democratic Party's nomination this year, but many political analysts say the sluggish economy means he faces a tough race against the eventual Republican nominee.