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Bluefin Capital Management LLC briefly popped up as the second-largest investor in United States Steel Corp. this week, the latest twist in an eventful year or so for the American steelmaker.

An asset manager is seeking to quash Nippon Steel's takeover of U.S. Steel and oust the leadership of the U.S. steelmaker after taking a stake in the company.

WASHINGTON/TOKYO -- U.S. President Donald Trump said Sunday that Nippon Steel would not be allowed to take a majority stake in U.S. Steel, making it highly likely the Japanese company will need to ...