The race for the Republican presidential nomination is about to take a big step forward, with 10 states weighing in Tuesday on the biggest day of voting yet in the two-month-old campaign.

With several key contests set for so-called "Super Tuesday" -- from the swing state of Ohio to the delegate-rich Georgia -- the four remaining candidates have pursued varying strategies for capitalizing on the day's voting and gaining momentum.

Mitt Romney remains the front-runner and could use a dominant showing Tuesday to all but eliminate doubt about his inevitability. But Rick Santorum continues to present a strong challenge, and polls have remained close in Ohio, a Midwestern industrial state where voters have an uncanny history of picking winners in presidential politics...