AMES, Iowa – Mitt Romney intensified a new – and, aides said, final – line of attack against President Obama on Friday, arguing that the incumbent who once stood for historic change has run a re-election campaign built around small ideas and trivial attacks.

Mr. Romney, speaking from a teleprompter to a crowd of 2,200 at a factory here, offered himself up as a 2008-like alternative to Mr. Obama.

“Four years ago, candidate Obama spoke to the scale of the times,” Mr. Romney said. “Today, he shrinks from it, trying instead to distract our attention from the biggest issues to the smallest — from characters on Sesame Street and silly word games to misdirected personal attacks he knows are false.”