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. 

“The U.S. has crafted the world trading system. We have led the formation of the world trading system as it stands now and I think there are some who are prepared to retreat from that leadership,” he said during a recent interview at the Finance Committee headquarters in the Dirksen Building.

“It’s not good for U.S. leadership and it’s not good for the economy,” he added.

Warren has diverged from the White House on several issues, like its focus on revamping NAFTA over launching new free trade deals. He also refutes Trump’s repeated assertions that the U.S. has a trade deficit with Canada.   

“That’s not the best way to look at our bilateral trading relationships with countries. Those trade deficits and trade surpluses exist for reasons that have very little to do with trade deals,” Warren said. “There should be more [free trade agreements], not spending our time either not doing FTAs or revising FTAs that we have.”

But in other areas, he offered more tepid praise, like on the administration’s attempts to push back against what Warren calls China’s “mercantilist policies that have caused great harm to U.S. business and U.S. workers.”

“There is a lot of interest here in working with the administration to craft a comprehensive strategy for dealing with Chinese economic policies,” he said. “The NAFTA negotiations are going to determine how much space the conference is prepared to give the administration to that policy.”

Watch: Trump Signs Steel and Aluminum Tariffs

Trade as a focal point

A onetime legal adviser at the World Trade Organization for the Office of the United States Trade Representative, Warren arrived at the Finance Committee in 2013 amid a whirlwind of trade activity.

The Obama administration was seeking fast-track authority to negotiate a multinational trade deal between the United States and 11 other Pacific Rim countries — the Trans-Pacific Partnership, or TPP.

But then came the 2016 presidential election, when trade became a key issue on the campaign trail. Trump, Hillary Clinton and Vermont Sen. Bernie Sanders, an independent who unsuccessfully challenged Clinton for the Democratic nomination, all made their opposition to the TPP a cornerstone of their respective platforms.

And as one of his first actions in the White House, Trump officially withdrew the U.S. from the trade pact, a disappointment for Warren.

“Unfortunately, we didn’t get TPP into the place where we needed it to be in order to pass Congress, which was very disappointing to me,” he said. “Partly because of the challenge posed by China, we do need to be reinforcing U.S. leadership in the region with our allies and other countries.” 

[TPP and Keystone Actions Unite Trump With Some Vulnerable Democrats]

Trump has said he would reconsider his decision if the deal could be made “substantially better.” But that appears unlikely at this point given that the other countries agreed earlier this year to move forward with the pact — and without the United States.

The Trump administration has also expressed interest in pursuing a number of bilateral trade deals, a departure from the traditional Republican orthodoxy that larger, multinational deals are inherently more beneficial to the U.S.

“In some cases, I think you can sit down with some countries bilaterally and perhaps have more leverage or have more room for creativity and come to a better deal,” Warren said. “Bigger is almost always better in this space, but if [Trump] thinks he can drive a better bilateral deal then I think that’s an acceptable way to go.”

Looming trade war?

Trump blindsided most congressional Republicans when the news broke last month that his administration would seek to impose import tariffs of 25 percent on steel products and 10 percent on aluminum products.

The move was met with swift criticism on Capitol Hill. And like his boss, Senate Finance Chairman Orrin G. Hatch, Warren had a strong critique of the decision. 

“It really looks like it was a choice to favor one small sector of the economy, the steel sector, at the expense of the rest of the U.S. economy,” he said. “That’s not trade policy, that’s industrial policy.”

[GOP Reaction to Trump Tariffs Is Fast, Furious and Negative]

The White House pursued the action under the guise of a seldom-used authority related to national security, which also rang alarm bells in Congress. 

“It is a Cold War-era statute that was directed at a Cold War environment, a true national security crisis,” Warren said. “For every trade issue the administration has identified, there is a trade tool available and those are the tools they should be using.”

While several countries have now been exempted from the tariffs, the action has left many on Capitol Hill jilted and worried about how the White House will approach a much more consequential decision: What to do with the future of NAFTA?

The trade agreement between the U.S., Mexico and Canada is a major economic driver in many states and a complete withdrawal would face significant congressional resistance.

Congress will have final authority to approve or reject any negotiated product. But concerns remain that the administration will ignore the will of many lawmakers in crafting an updated pact.  

Warren himself shot off a warning to the White House should they pursue such a route.  

“The lesson of less-successful trade agreements, or trade agreements that did not ultimately win congressional approval, is that congressional views about how that agreement should look in the end were not always heeded as closely as they should be,” he said.

In terms of the administration’s engagement with Congress so far, specifically the Office of the United States Trade Representative, Warren called it “reasonably good.”

“There’s certainly room for improvement, especially in the context of ongoing trade negotiations, but overall I’d give them pretty good marks,” he said. 

With nearly nine months left before Hatch’s retirement from the Senate, Warren said he will be focused on shaping trade policy “in what we think is the best direction.”

“We’ll try to use that time wisely to enact the chairman’s preferences for trade policy,” he said.