DES MOINES, Iowa - Republican front-runner Mitt Romney and US Representative Michele Bachmann led a closely watched presidential poll of Iowa Republicans, the state that holds the first contest in the nomination battle.

The Iowa caucuses, often held on a frigid winter night that can limit turnout to those most committed, often serve to winnow the field of candidates.

Whoever captures the nomination in the unsettled Republican field is expected to challenge Democratic President Barack Obama in the November 2012 general election.