WASHINGTON (AP) — Mitt Romney’s campaign is working hard to chip away at President Barack Obama’s advantage among early voters, and there are signs the effort is paying off in North Carolina and Florida, two competitive states that the Republican nominee can ill afford to lose. Obama is doing better in Iowa, another battleground state important to both candidates.

Obama dominated early voting in key states four years ago, giving him a big advantage over Republican John McCain before Election Day even arrived. In Colorado, Florida, Iowa and North Carolina, Obama built up such big leads among early voters that he won each state despite losing the Election Day vote, according to voting data compiled by The Associated Press.

Romney’s campaign won’t predict victory among early voters this year. But a top campaign official is adamant that Romney will not let Obama build insurmountable leads among early voters in key states.