Turkey delivers just 4 percent of steel mill imports, valued about $1.18 billion past year, according to the US Department of Commerce.
In his tweet about the new tariffs, Trump said "Our relations with Turkey are not good at this time!".
Since then, its relationship with Turkey, the sixth largest steel importer to the United States, has deteriorated, prompting Ankara to send a delegation this week to Washington to meet with both the State and Treasury Departments.
Turkey exported $1.04 billion (€0.91 billion) worth of steel and $60 billion worth of aluminum to the USA in 2017, according to the Hurriyet newspaper.
The Turkish President, Recep Tayyip Erdogan, took a combative stance in an earlier press conference, pledging to "overcome this economic war". Mr Brunson denies the charge.
"Their currency, the Turkish lira, slides rapidly downward against our very strong dollar!" It fell yet further to 6.2 to the dollar at 1254 GMT, almost 12 percent weaker on the day. Brunson was among many foreign nationals detained by Turkish President Erdogan in the wake of a failed 2016 coup attempt. Thus, Trump's tweet suggests that any country that enters a time of economic turmoil - and consequently, sees the value of its currency fall - is a fair target for punitive trade actions by the United States.
Watch NASA’s historic Sun probe mission launch: here’s how
Sixty years ago, a young astrophysicist at the University of Chicago, Eugene Parker , proposed the existence of solar wind. During its elliptical orbit, the Parker Solar Probe will make it up to 430,000mph, which would be a new speed record.
The Brunson dispute triggered the collapse in the Turkish currency as investors feared US financial sanctions.
The defiant tone and war rhetoric only hurt the lira more, before Erdogan's finance chief and son-in-law, Berat Albayrak, tried to ease investor concerns during a conference, saying the government would safeguard the independence of the central bank.
"Unless the United States starts respecting Turkey's sovereignty and proves that it understands the dangers that our nation faces, our partnership could be in jeopardy", Erdogan said.
Washington this month imposed sanctions on senior Turkish officials, angering President Recep Tayyip Erdogan and prompting retaliatory measures by Ankara.
The diplomatic tension and the failure of Turkish officials to persuade the United States to lift the sanctions plunged the lira to new lows this week.
One of the triggers of the turmoil has been a standoff with the US over detained American pastor Andrew Brunson. The U.S. responded by slapping sanctions on Turkey and threatening more.
On August 1 Washington announced sanctions against Turkey's justice and interior ministers, prohibiting U.S. entities and citizens from doing business with them, after threatening to impose "large sanctions" if Ankara failed to free Brunson.
In the City, fund managers and investment commentators warned of the risk of capital flight from the country and flagged up the risk to European banking stocks - such as Spanish lender BBVA and Italian group UniCredit - from their exposures to Turkish lending. One economically-illiterate leader is crippling his own economy and blaming everyone else for it, which then turned out to be partially correct when another economically-illiterate leader made a decision to cripple their economy as payback for what they have done to themselves.