– Robert Lighthizer just became one of the most powerful people in Washington.

Lighthizer, the U.S. trade representative, will spend the next 14 days deciding which countries, if any, will be exempt from the stiff and sweeping steel and aluminum tariffs that President Donald Trump authorized on Thursday.

The issue is expected to dominate discussions in Brussels on Saturday between Lighthizer and his trade counterparts in Japan and the European Union, with the European trade commissioner saying on Thursday that Europe should be excluded. Dozens of other countries that import metals into the United States — such as Brazil, the United Arab Emirates and South Korea — are demanding a carve-out or threatening retaliation if they are included.

It is a fight Lighthizer has been preparing for his entire life.

Lighthizer, 70, grew up in a well-off family in a Midwest town that did not share his fortune. Ashtabula, Ohio, a port town on Lake Erie, saw its surrounding steel mills shutter and decline as factories automated and moved abroad. The decimation of local manufacturing shaped his views on trade, friends said, hardening his approach and leading him to become a skeptic of globalization.

In the 1980s, he brought that skepticism to Washington where, as deputy trade representative for President Ronald Reagan, he wielded the threat of tariffs to persuade Japan and other countries to cut their steel shipments to the United States. A lawyer by training, he continued his defense of American industry after his government stint, filing lawsuits on behalf of American steel giants like United States Steel, who claimed they were withering from foreign competition and sought government protection from what they saw as unfair practices abroad.

In the intervening years, Lighthizer has embraced the view that countries like China, South Korea and Mexico have bent or broken global trade agreements to take business from the United States, generating worrisome trade deficits and weakening American manufacturing.

To reverse the trend, Lighthizer is trying to rewrite global trade rules in the United States’ favor. He has found his trade policy soul mate in Trump, who has elevated Lighthizer’s role and given him his blessing to embark on an unapologetic mission to take away advantages from countries and systems that both men believe have cheated the United States.

That includes preparing a major trade action against China, which Lighthizer has been working on for months and will be aimed at curbing intellectual property theft. It includes efforts to overhaul the World Trade Organization, which trading partners describe as a plan to strip away that organization’s power and clout. But, mostly, it includes sprawling and contentious negotiations with South Korea over the future of its trade deal with the United States and, especially, with Canada and Mexico over the future of the North American Free Trade Agreement.

Trump has dangled the potential for the two trading partners to be permanently exempt from the steel and aluminum tariffs, as long as they agree to a NAFTA deal that satisfies U.S. demands. What that means, exactly, remains to be seen. The three countries have already been through seven rounds of negotiations over revising the 1994 pact, with little progress to show for it and fairly intractable views on several major provisions.

Lighthizer had a mixed view of the tariffs, supporting the plan during meetings in the Oval Office, but privately expressing concerns that broad measures could target allies rather than the real culprit, China, according to people familiar with his views who were not authorized to speak publicly.

Like his boss, Lighthizer views China as the biggest offender in the global trading system, accusing the country of using state subsidies to build more factories than it needs and calling China’s trade practices an “unprecedented” threat to the world trading system. He is spearheading an initiative to combat China’s alleged theft of American trade secrets, an effort that may include tariffs on Chinese products and restrictions on Chinese investment flowing into the United States.

At times, Trump seems to have taken his China-bashing language straight from Lighthizer, including in late February when the president blamed the World Trade Organization for China’s rise.

It is that combination of nationalist instincts and keen understanding of trade law that has aided Lighthizer’s rise in the White House. Trump originally envisioned Wilbur Ross, the commerce secretary, as his trade czar and the person to coordinate trade policy across the government. But Ross drew the ire of the president as he failed to negotiate a sufficiently tough deal with the Chinese and faced allegations that he had inflated his wealth.

Lighthizer has emerged as the indispensable adviser, espousing the type of get-tough views on China and other countries that were red meat to Trump.

“By virtue of his abilities, Lighthizer’s profile is rising,” said Gary Hufbauer, a senior fellow at the Peterson Institute for International Economics. “His own description might be that he’s very keen on seeing that the rights of U.S. firms are not trampled on, and that international competition is fair and balanced. To my way of thinking, that adds up to a polite way of saying ‘protectionist.’ ”