When President Donald Trump fires up his Twitter account to talk trade, it is Shane Warren who is left to explain his posts to the Senate Republican Conference.

As the GOP’s chief international trade counsel on the Senate Finance Committee, Warren is helping to shape the chamber’s trade agenda at a time when Republicans control both Congress and the White House. But like many current jobs in Washington, working in a position subject to Trump’s whims presents its own set of challenges.

From imposing new tariffs on steel and aluminum products to renegotiating the North American Free Trade Agreement and ramping up tariffs against China, Trump is upending the global trade environment and bucking traditional Republican trade policy along the way.

He is also stoking fears of a trade war, concerns that were exacerbated on Monday when China announced it would impose retaliatory tariffs on more than 130 U.S. goods, including pork.

Like many Republicans, Warren was critical of both the tariff decision and the mechanism under which the administration implemented them. While he praised some actions by the White House — like the move to crack down further on Beijing’s questionable trade practices — Warren offered a measured criticism of Trump’s overall trade agenda.