President Barack Obama now holds slight lead over Mitt Romney

After a dead-heat race for months, President Barack Obama is narrowly leading Republican challenger Mitt Romney in major polls, both nationally and in key states.

Some of the edge could be a bounce from the Democratic convention, and such lifts are subject to fading. But both campaigns are paying close attention to any shift in the polls since there's been so little movement all summer, and they're adjusting their campaign strategies accordingly.

Romney, coming off two rough weeks, was addressing the U.S. Hispanic Chamber of Commerce in Los Angeles, a fast-growing crucial voting bloc that Obama won in 2008 and continues to favor him now.

At the same time, Romney's campaign was launching a new advertising offensive emphasizing the GOP nominee's plans to lift the economy rather than just focusing on slamming Obama.

"My plan is to help the middle class," Romney says, speaking directly to the camera. "Trade has to work for America. That means crack down on cheaters like China. That means open up new markets."

Romney has accused Obama of policies that resulted in U.S. jobs being shipped to China. The Obama campaign blames Romney's former equity firm for doing the same thing.

Almost if on cue, the Obama administration on Monday sought a World Trade Organization ruling telling China to stop subsidizing auto parts made for export. It argues the practice undercuts manufacturers in Ohio and elsewhere and encourages U.S. companies to outsource.

And, not coincidentally, Obama had campaign rallies Monday in Cincinnati and Columbus, Ohio

Ohio is a crucial swing state, as it has been for the last several elections, and no Republican has ever won the presidency without carrying it.

Seven weeks out, Obama leads Romney in Ohio, Florida and Virginia, according to NBC News/Wall Street Journal/Marist polls in those states.

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