Several of those exporters-Canada, Turkey, and Germany-are members of the North Atlantic Treaty Organization (NATO) and as such the Trump administration may have to show that their strategic partners in the military alliance are somehow threatening USA national security interests.
Chancellor Merkel, for whom the summit is an opportunity to show off her diplomatic skills ahead of a federal election in September, welcomed the first face-to-face meeting of Trump and Russian President Vladimir Putin on Friday.
The U.S. now has 28 anti-subsidy tariffs on Chinese steel, including several imposed under President Obama.
The G-20 comprises Argentina, Australia, Brazil, China, Germany, France, Britain, India, Indonesia, Italy, Japan, Canada, South Korea, Mexico, Russia, Saudi Arabia, South Africa, Turkey, the USA and the European Union.
The U.S. has often criticized China for illegally subsidizing the steel and aluminum industries and contributing to a global glut of the metals.
Advocates for efforts against global warming expressed relief that the other countries had remained unanimous in support of the Paris accords.
But even amid continued engagement, major breakthroughs look less likely with President Xi Jinping complaining of a "negative" turn in relations just before his expected meeting with Donald Trump this week, and escalating tension over North Korea that the USA links to trade.
Also, invoking national security is all but taboo at the World Trade Organisation, the arbiter of worldwide trade rules, because it is largely seen as a way to wage economic warfare by citing arbitrary defense concerns.
A day after Trump slammed Moscow's actions in Ukraine and Syria, the two men had a "robust and lengthy exchange" about allegations of Russian meddling in the 2016 U.S. election, Secretary of State Rex Tillerson said. His point was that it doesn't make sense to talk about bilateral trade deficits in a multilateral world, the official said.
"There was a question mark there, as to whether or not the EU. would be able to continue signing free trade agreements in the future", said André Sapir, an worldwide trade expert and a former economic adviser to the European Union's Director General for Economic and Financial Affairs.
Some of the other countries at the summit rebuked the USA for Trump's decision to pull out of the Paris climate accord. "So that was kind of dissonance between the position of United States and position of all other countries".
"International trade and investment are important engines of growth", the G-20 leaders said. That is why steel-consuming companies in the United States, and many of his own more prudent advisers, are urging Trump not to act as if the US national interest were equivalent to the narrow interests of the protection-craving steel industry.
"Getting ready to leave for Poland, after which I will travel to Germany for the G-20".
Participants face a USA leader much more unpredictable than his predecessors, which may concern the Chinese as tempers fray on how best to curtail North Korea's nuclear ambitions.
The exchange illustrates the world's struggle to come to terms with the Trump era and his administration's determination to remold the postwar global consensus in favor of the U.S. The last major summit, of G-7 leaders in May, ended with the U.S. isolated on climate change. "Perhaps China will put a heavy move on North Korea and end this nonsense once and for all!" But he has since shown signs of losing patience as Pyongyang tests missile after missile, including what the U.S. said was its first intercontinental ballistic missile on Tuesday.
She has been more outspoken than most of her counterparts from other European countries. Global leaders have seen an opening in persuading Trump to change course, as he made a last-minute decision to renegotiate, rather than withdraw, from NAFTA after intense pressure from Canada and Mexico. But the deal faced opposition in Congress under Obama, and Trump formally ended its chances when he withdrew the US from the deal upon taking office. These developments affect the BRICS nations - Brazil, Russia, India, China and South Africa - and reinforce the need to step up coordination "to speak in one voice to steer the world economy in right direction", he said. A Defense spokesman did not confirm or deny whether the department might be engaged in its own assessment of the impact of imports on national security.style="text-align: center;"