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But attention still centers on Mr. Romney, who has struggled during the campaign to unite Republican voters, but has still amassed some impressive wins.

His come-from-behind victories in Ohio and Michigan primaries showed he maintains significant strength in the industrial Midwest.

In blasting Mr. Obama on Monday, Mr. Romney said the administration’s heavy-handed web of tax, spending and regulatory policies is crushing the innovation and financial risk-taking needed for a strong economy. To drive home the point, he suggested that some of the nation’s most legendary entrepreneurs would have suffocated under the weight of today’s federal government.

He added that “a regulator would have shut down the Wright Brothers for their ‘dust pollution.’ And the government would have banned Thomas Edison’s light bulb.”

“Oh, yeah,” he quipped, recalling a law designed to phase out the old-style incandescent bulb, “Obama’s regulators actually did just that.”

The light-bulb change actually was passed by Congress in 2007 and was signed into law by Mr. Obama’s Republican predecessor, President George W. Bush.