President Trump's tariffs have notably increased the price of aluminum for U.S. businesses and consumers, a study provided first to Axios shows.Why it matters: Trump has insisted the cost of the tariffs would be borne by China and other exporters, but the data shows that Americans are paying the costs."It’s pretty safe to say that it's 100%," Douglas Holtz-Eakin, president of think tank American Action Forum and a former director of the Congressional Budget Office, tells Axios.Background: The price of aluminum worldwide spiked in April after the Treasury Department put sanctions on Russian producer Rusal, following Trump's announcement of 10% aluminum tariffs on every country (with exceptions eventually carved out for allies like Australia, Canada and Mexico).Those price increases have since unwound in global markets, but U.S. customers continue to pay higher prices, as shown by the so-called Midwest Premium.The price increase appears to line up very closely with the 10% tariffs imposed by Trump.The intrigue: Trump on Friday doubled down on the aluminum tariffs, adding derivative aluminum products such as nails, tacks, staples, wire and parts for cars and tractors, meaning more price hikes are likely on the way.The bottom line: "There have been assertions that China is paying the tariffs," study co-author Holtz-Eakin says. "And that’s not true."Go deeper:Macron and Trump call ceasefire on digital taxes and wine tariffsThe "phase one" deal isn't all that it seemsManufacturing should bounce back in 2020