COUNCIL BLUFFS, Iowa (AP) – Republican presidential candidate Mitt Romney is shifting his Iowa campaign into a more aggressive phase, launching his first TV ads in the state with a spot in which he declares he knows about how economies grow. In the 30-second spot set to begin running Friday, Romney says the right answer for America is to stop the growth of the federal government and to start private-sector growth. Romney’s decision to start spending money on paid advertising in Iowa just five weeks before the Jan. 3 caucuses signals a belief that he can fare well in the state even though his 2008 bid was tripped up there. The move comes as former House Speaker Newt Gingrich has emerged as Romney’s chief challenger for the nomination.