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A former Reagan administration official is expected to be picked as President-elect Donald Trump's U.S. trade representative, according to a senior transition official.

Robert Lighthizer will help spearhead Trump’s push for tougher policies against China and Mexico. He has long pushed for stiffer tariffs on foreign imports.

Related: Why a Trump Trade War With China Might Hurt America

Trade was a key campaign issue for Trump, who railed against deals like NAFTA and the Trans-Pacific Partnership (TPP).

Lighthizer is a former deputy U.S. trade representative under President Ronald Reagan.

Trump now has three major posts left to be filled: secretary of veterans affairs, secretary of agriculture, and director of national intelligence.