MUSCATINE, Iowa (AP) — Trailing in Iowa, Republican presidential hopeful Mitt Romney intensified his criticism of rival Mike Huckabee on Thursday and called him "too liberal" on immigration, crime, spending and taxes.

"I frankly think that the more people come to know Mike Huckabee the more they realize they don't know about Mike Huckabee," the former Massachusetts governor said a day after all the candidates largely held their fire at their final debate before Iowa's Jan. 3 caucuses.

Romney, however, pulled no punches after talking fiscal issues with prospective supporters at a historic hotel in this eastern Iowa town along the Mississippi River. Speaking to reporters, he vowed to keep up his review of the former Arkansas governor's record.

The stepped-up rhetoric comes as polls show a competitive race in the first state to speak in the state-by-state march to the GOP nomination. Romney led in the state for months, but Huckabee's recent rise here and elsewhere has prompted Romney to aggressively go after his opponent in TV ads and on the campaign trail this week as the race has grown hotter by the day.