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Mitt Romney accused President Obama of Tuesday of adding "insult to injury" with his proposal to raise taxes on families making more than $250,000, calling the move a tax hike on "job creators" at a time of weak economic growth.

A day after Obama unveiled his tax proposal and urged lawmakers to act, the debate moved quickly to the presidential campaign trail. As Romney hammered the president at a town hall in the battleground state of Colorado, Obama rallied a crowd in Cedar Rapids, Iowa, in support of his plan.

"To give me another tax break or to give Warren Buffett another tax break or to give Mitt Romney another tax break -- that would cost about a trillion dollars, and we can't afford it, not at a time when we're trying to bring down our deficit," Obama said, adding he's not trying to "punish success."

The president wants to extend the Bush-era tax rates for everyone making less than $250,000 but let them expire for those making more than that. The tax rates are set to expire for everyone at the end of the year unless Congress acts. Obama told the Iowa crowd Tuesday he wants to stop the tax hikes for the "98 percent of Americans" who are "just like you."

But Romney said the president just doesn't understand "how this economy works."

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    The Republican presidential candidate accused Obama of trying to make it harder for businesses to create jobs, calling the tax hike an "extreme liberal" idea. He said it adds "insult to injury" following another monthly jobs report showing weak growth in June.

    Earlier in the day, Republican National Committee Chairman Reince Priebus told Fox News that the president's proposal is a "sham" that, if enacted, would cut into already meager economic growth. He accused Obama of playing a "divisive rich-versus-poor game."

    Obama has drawn a line in the sand over the tax rates, vowing to veto any bill that extends the tax rates for everyone.

    In his earlier remarks at the White House on Monday, Obama argued that sustaining the current tax rates for top earners puts too big a hole in the federal budget, saying "we can't afford to keep that up." Obama called on Congress to extend those rates, for one year, for families earning less than $250,000 -- failure to do so, he said, would be a "blow" to families and a "drag" on the economy.

    "We don't need more top-down economics," Obama said. "We need policies that grow and strengthen the middle class."

    The proposal pre-empts a more sweeping proposal from congressional Republicans, who are calling for an extension of the Bush tax rates for everyone.

    GOP lawmakers rebuked the president. House Speaker John Boehner accused Obama of "doubling down on his quixotic call for the same small businesses tax hikes that have been routinely rejected by the House and Senate."

    The proposal comes as Obama courts the blue-collar vote in key battleground states like Ohio and Pennsylvania, where he has talked frequently about middle-class values.

    The shift to the tax issue also comes after last week's dismal jobs report that showed the country's jobless rate stuck at 8.2 percent in June.