DES MOINES, Iowa (AP) -- Republican presidential candidate Mitt Romney is defending a TV ad that quotes President Barack Obama out of context, signaling he's ready for bare-knuckled campaigning despite sharp complaints from Democrats and some neutral observers.

Romney said while campaigning in Iowa Wednesday that the ad is fair game, and underscores how the former Massachusetts governor stressing his decades in the private sector intends to confront the president if Romney is the GOP nominee next year.

The ad which began airing in New Hampshire Tuesday uses audio of then-Sen. Obama campaigning in the state in 2008, saying: "If we keep talking about the economy, we're going to lose."

The ad omits any acknowledgement that Obama was quoting the campaign of his opponent, 2008 GOP nominee John McCain. Instead, the ad leaves the impression that it is Obama who does not want to discuss the economy.

Romney told reporters in Des Moines his campaign distributed the ad with a press release noting the words were originally from Obama's opponent.

"There was no hidden effort on the part of our campaign. It was instead to point out that what's sauce for the goose is now sauce for the gander," Romney said, after addressing more than 300 employees of a downtown insurance company. "This ad points out, now, guess what, it's your turn. The same lines used on John McCain are now going to be used on you, which is that this economy is going to be your albatross."

It's a more aggressive tone for Romney, who all along in his second bid for the GOP nomination has cast himself as the field's most prepared candidate to tackle the economy. Now, he is signaling that he'll pull no punches with Obama.

"How we will beat President Obama is by speaking day in and day out about the one topic he does not want to talk about. And that's the economy," Romney said, with U.S. Sen. John Thune, a South Dakota Republican who endorsed him Wednesday, by his side. "If I'm the nominee, he'll be trying to take me apart."

Democrats roundly criticized the ad as misleading.

PolitiFact, a non-partisan campaign watchdog, referred to the ad's use of Obama's past comment as "ridiculously misleading," and noted the campaign could have conveyed the point that the tables had turned on Obama "without distorting Obama's words."

Romney's appearances in Iowa Wednesday reflect his recent stepped-up his activity in the state that will hold the first caucuses on Jan 3.

While just his fifth visit to the state this year, it was his third in about a month.

In the meantime, his small campaign staff has grown modestly, been in regular touch with the statewide network of supporters he has held onto since his second-place finish in the 2008 caucuses. He is organizing a series of telephone question-and-answer sessions with thousands of Iowans, and is planning to unveil campaign ads in Iowa soon.

He still has not appeared with his Republican competitors in the state, having skipped three events over the past month.

Romney has said he plans to debate his GOP rivals in Iowa. There are debates scheduled December 10 in Des Moines and five days later in Sioux City.

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