WASHINGTON (AP) — Republican presidential nominee Mitt Romney is shifting sharply to the political center as he begins to deliver a closing argument aimed at a slice of moderate, undecided voters a month before Election Day.

On taxes, immigration and more, the former Massachusetts governor has toned down his heated, campaign trail rhetoric this week, including during his strong debate performance Wednesday night, as he looks to gain ground against President Barack Obama in the handful of states that will determine the outcome of the competitive race.

"I know this is going to be a close-fought battle," a jubilant and invigorated Romney said in Colorado before he flew to Virginia for an evening rally with running mate Paul Ryan.