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CINCINNATI — With 12 days left until the election, Mitt Romney began offering the outlines of a closing argument here that co-opts President Obama’s message from four years ago, repeatedly promising to deliver “big change” at a moment of “big challenges” and calling his opponent a guardian of the status quo.

Mr. Romney, who has narrowed Mr. Obama’s lead in state and national polls, started a bus tour across Ohio by casting himself and his running mate, Representative Paul D. Ryan, as reformers prepared to correct America’s course, by reining in debts, salvaging Medicare and reducing taxes.

“These challenges are big challenges,” Mr. Romney said. “This election is therefore a big choice. And America wants to see big changes, and we’re gonna bring big changes to get America stronger again.”

The speech highlighted how significantly the Romney campaign’s pitch to voters has evolved since he entered the race in 2011. Back then, he devoted much of his time berating the president, and mocked the idea of big change: a standard line back then Mr. Obama for trying to “transform America.”

On Thursday, it was Mr. Romney who called for “big change,” of the small-government variety, a dozen times, saying that Mr. Obama stood for “the status quo path.”

“The path we’re on — the status quo path — is a path that doesn’t have an answer about how to get the economy going,” he said. “The president has the same old answers as in the past — he wants another stimulus, he wants more government workers, and he wants to raise taxes.”

The Obama campaign scoffed at Mr. Romney’s adoption of their language from four years ago.

“The only ‘change’ that Mitt Romney has promised is bringing back the failed policies that caused the economic crisis and putting a rubber stamp for the far-right wing in the White House,” said Lis Smith, a spokesman for the president’s campaign. “Americans understand that’s not ‘change’ that they can afford.”

Mr. Romney appeared to be testing new language as he prepared for a major speech about the economy, which he is to deliver in Iowa on Friday, as he seeks to build on the energy he generated from a series of animated debate performances.

In a dig at the president, Mr. Romney said the debates “had diminished the Obama campaign,” which he said had resorted to invoking “Sesame Street” characters, like Big Bird, and playing “word games.”

Mr. Romney is traveling on Thursday to three cities in Ohio, whose 18 electoral votes could swing the outcome of a close presidential campaign. After Cincinnati, he heads to rallies in Worthington and Defiance.