(CNN) -- A day after losing the first presidential debate, President Barack Obama and his campaign accused his Republican challenger Mitt Romney of being dishonest about tax policy and other issues. "If you want to be president, you owe the American people the truth," Obama said at a campaign rally Thursday in Denver. "So here's the truth: Governor Romney cannot pay for his $5 trillion tax plan without blowing up the deficit or sticking it to the middle class. That's the math." Romney's pledge: No tax cut for the rich The president's top aides were even more blunt. "Romney's performance was one that's probably unprecedented in its dishonesty," senior adviser David Plouffe told reporters.
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NEW: Ryan, Romney say debate offered voters a clear choice
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The Obama campaign says Mitt Romney was dishonest
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Republicans crow about the first debate; Democrats downplay it
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Analysts and a snap poll say Mitt Romney won the opening round
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Obama joked Thursday that a different @placeholder appeared at the debate from the conservative candidate who won a grueling primary campaign to challenge him on November 6.
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"When I got on to the stage I met this very spirited fellow who claimed to be Mitt Romney," @placeholder said told the crowd of more than 12,000 at a Denver park.
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@placeholder criticized Obama's record and depicted the president's vision as one of big government, while the Democratic incumbent defended his achievements and challenged his rival's prescriptions as unworkable.
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But Romney came off as the more energized candidate overall by repeatedly attacking Obama on red-meat issues for @placeholder such as health care reform and higher taxes, while the president began with lengthy explanations and only later focused more on what his opponent was saying.
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The former governor's strongest moments came in criticizing @placeholder's record, saying the nation's high unemployment and sluggish economic recovery showed the president's policies haven't worked.