CNN

John McCain attends an event on the aircraft carrier Yorktown in Mount Pleasant, South Carolina, on Friday.

(CNN) - Voters head to the polls and caucus sites Saturday in South Carolina and Nevada, contests that could propel two candidates to front-runner status in this year's wide-open presidential races.

A win in the South Carolina Republican primary could give one of the candidates a hand up in a race that, so far, has produced three different winners in three major contests.

Historically, the path to the Republican nomination has gone through South Carolina, which relishes its role of being the political gateway to the South.

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