CINCINNATI - Looking to bolster his standing with blue-collar voters, President Obama has for the second time in as many months filed suit against China for unfair trade practices on the eve of a major campaign swing through the nation's manufacturing belt.

The White House said the complaint, filed with the World Trade Organization, accuses China of $1 billion in illegal subsidies for exports of cars and car parts. It will be a focus of Obama's pitch today on a visit to Ohio, officials said. In July Obama lodged a similar case at the WTO to coincide with a three-day Ohio bus tour, alleging unfair Chinese duties on more than $3 billion in U.S. auto exports.

The administration claims the subsidies and duties have disadvantaged American companies competing in the same markets as Chinese firms and imperiled U.S. workers' jobs.

The latest case, demonstrating the power of incumbency to create a fresh talking point for Obama, comes as he seeks to shift attention back to the economy after a week of headlines dominated by foreign policy . It's also squarely aimed at voters in key manufacturing-dominant regions of swing states, where China is seen as one of the biggest threats to profits and growth.

The auto industry in Ohio, including suppliers of raw materials like steel and plastics, accounts for more than 12 percent of the state's total employment, or roughly 850,000 jobs. Auto parts manufacturers employ 54,200 Ohioans alone, the administration says.

Republican presidential nominee Mitt Romney, who has also been fiercely courting the same voters, called Obama's announcement too little too late.

"Campaign-season trade cases may sound good on the stump, but it is too little, too late for American businesses and middle-class families," Romney said in a statement. "President Obama's credibility on this issue has long since vanished. I will not wait until the last months of my presidency to stand up to China, or do so only when votes are at stake. "

His campaign has been attacking Obama on the stump and in television ads as failing to take a harder line against the Asian power.

The latest Romney ad, airing in Ohio and other battlegrounds, suggests Obama has not aggressively held China to account under international law. "Trade has to work for America. That means crack down on cheaters like China," Romney says in the ad. The Republican's campaign also claims skyrocketing debt during Obama's term has made the U.S. more beholden to the China, the top foreign lender.

"Four years ago, candidate Obama promised Ohioans he wouldn't run up the debt by borrowing from China. As he returns to Columbus today, the President has amassed over $5 trillion in new debt that's held by countries like China and… has shown an abject failure of leadership on the issue," said Romney spokeswoman Amanda Henneberg.

The Obama campaign is running advertisements rebutting Romney's claims, portraying the former Bain Capital corporate buyout specialist as personally working to outsource U.S. work to China while retaining financial investments in Chinese companies.

The candidates' jabs at each other over China policy come as Obama appears to hold a solid lead over Romney in crucial Ohio, according to several recent polls. No candidate for president since 1960 has won the White House without winning Ohio.

Likely Ohio voters prefer Obama to Romney by a 50 to 43 percent margin in the latest Wall Street Journal/Marist/NBC survey. The president also holds an edge on handling of the economy, with voters seeing him as more likely to do a better job than Romney, 48 to 44 percent.

Obama has filed a total of eight cases against China at the WTO during his first term.

This post has been updated.

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