The Trump administration has assessed $4.4 billion worth of duties on steel and aluminum imports and a range of goods from China under the tariffs it imposed in an effort to protect U.S. companies.

A spokesman for the Department of Homeland Security told the Washington Examiner that importers owe the federal government $4.4 billion for importing goods hit by the tariffs through Oct. 2, but said it was unclear how much of that total has been collected. The Treasury Department didn't have details on what portion of the $4.4 billion had been collected, and how much was still owed.

Still, the assessments show that the tariffs are imposing a real cost to importers, who are responsible for paying the charge.

Trump got aggressive on trade earlier this year, when he hit all U.S. trading partners with a 25 percent tariff on their exported steel and a 10 percent tariff on aluminum.

According to DHS, U.S. Customs and Border Protection had assessed $2.34 billion in duties on steel imports and $615 million on aluminum.

Trump followed that up with a 25 percent tariff on $50 billion worth of imports from China, to retaliate against China's failure to protect U.S. intellectual property rights, and its policy of forced technology transfer. He then hit another $200 billion worth of Chinese goods with a 10 percent tariff that could rise to 25 percent next year.

CBP said those tariffs against China have led to duty assessments of $1.45 billion against goods from China as of early October.

Even relatively small tariff hikes on goods can prompt importers to stop importing those goods altogether, especially in competitive industries. To the extent trade still happens, the assessed duties flow back to the U.S. Treasury, a point President Trump has made in several speeches around the country.

"So we're doing very well in our situation with China on trade. I have a great relationship with the president of China, President Xi. But it's got to be a two-way street. It — for 25 years and longer, it was not. And trillions and trillions of dollars was taken out of the United States for the benefit of China. We just can't have that. We have to make it fair."

"So we're at $250 billion now, at 25 percent interest," Trump said last month as he talked about the tariffs against China. "And a lot of money is coming into our coffers."

Federal revenue from Trump's tariffs are likely to continue growing. Trump's steel and aluminum tariffs are still in effect, as are the tariffs against China, which will rise from 10 to 25 percent in January unless the two countries reach an agreement to settle the trade fight.

Today, the tariffs are hitting about half of the goods China sends to the U.S., and Trump has threatened to go further by hitting the other half.