2 January 2012 Last updated at 16:19 ET

In pictures: Iowa caucuses

Former Massachusetts Governor Mitt Romney greets supporters at an event in Davenport, Iowa, 2 January 2012

Candidates are in the home stretch before Iowa votes to choose the next Republican nominee. One day before voting, former Massachusetts Governor Mitt Romney maintains a slim lead over his rivals.

Former Pennsylvania Senator Rick Santorum speaks to a crowd in Polk City, Iowa, 2 January 2012

Also fighting for the top spot is former Pennsylvania Senator Rick Santorum, a social conservative who is appealing to the evangelical Christian vote and has campaigned extensively in Iowa for months. His ratings, previously in single figures, have soared in recent weeks.

Former House Speaker Newt Gingrich addresses a crowd in Independence, Iowa 2 January 2012

With Rick Santorum rising, former House Speaker Newt Gingrich has seen his support slip in the face of a barrage of attack ads in recent weeks. He is fighting to get back into the top tier of candidates and secure a good finish on Tuesday.

Texas Representative Ron Paul delivers a campaign speech in Des Moines, Iowa, 2 January 2012

Meanwhile, Texas Representative Ron Paul, a libertarian-leaning candidate, is packing in as many as five events on his final day of campaigning in Iowa. Mr Paul is the only candidate who returned to his home state over the new year weekend.

A man covers his shirt in buttons for Texas Representative Ron Paul in Des Moines, Iowa, 2 January 2012

Ron Paul has a strong following in Iowa, and correspondents expect his supporters to turn out at the polls - a factor that could benefit him disproportionately in the event of bad weather.

Former House Speaker Newt Gingrich addresses a crowd in Walford, Iowa, 2 January 2012

While voter turnout can be rather unpredictable, analysts are expecting about 120,000 Iowans to cast votes on Tuesday at their local caucus. The meetings are held in schools, libraries, town halls and even private homes across the state.

Texas Governor Rick Perry meets supporters at Sioux City, Iowa 2 January 2012

Trailing the pack are Texas Governor Rick Perry and Minnesota Congresswoman Michele Bachmann, both social conservative candidates who enjoyed brief spells of popularity earlier in the campaign season but have struggled to maintain momentum.