At midday on Wednesday, the benchmark S&P/ASX200 index was down 27.2 points, or 0.32 per cent, to 8,565.3, while the broader All Ordinaries lost 25.5 points, or 0.29 per cent, to 8,803.2.
Overnight, the US president said drug manufacturers would be given a year or so to move manufacturing to the US, otherwise they would "tariffed at a very, very high rate, like 200 per cent".
Mr Trump also flagged the White House would be imposing 50 per cent tariffs on copper, which Commerce Secretary Howard Lutnick said could begin at the end of July or start of August.
Copper prices surged after the comments, ending the trading day up 13.1 per cent for their strongest one-day gain since 1989.
Australia is a major copper producer but exports very little to the United States, with most going to China and other Asian-Pacific countries. The US gets most of its copper from Chile.
"The idea is to bring copper home, bring copper production home," Mr Lutnick said later on CNBC.
IG analyst Tony Sycamore said that encouraging domestic copper production was a challenging objective given the complexities of relocating a copper mine.
At midday, seven of the ASX's 11 sectors were lower, with financials flat and energy, consumer discretionary and utility shares collectively higher.
The materials sector was down 0.6 per cent, with the iron ore giants higher and goldminers down as the price of the yellow metal dropped to a one-week low of $US3,310 an ounce.
BHP was up 0.4 per cent, Fortescue had added 0.7 per cent and Rio Tinto had advanced 0.6 per cent, while Northern Star was down 4.1 per cent, Evolution had retreated 8.8 per cent and West African Resources dropping 4.6 per cent.
Sandfire Resources, the largest copper-focused miner on the ASX, was down 3.8 per cent, while Capstone Copper Corp had retreated 2.9 per cent.
In the energy sector, uranium explorers and producers were under pressure, with Bannerman Energy falling 7.9 per cent and Deep Yellow retreating 7.1 per cent.Â
In the financial sector, the big four banks were mostly higher. Westpac had added 0.8 per cent, ANZ was up 0.2 per cent and NAB had advanced 0.4 per cent. CBA was the outlier, dropping 0.2 per cent.
In real estate, Lifestyle Communities had plunged 36.2 per cent to an eight-year low of $4.495 after a Victorian tribunal found the land lease operator breached the state's tenancy laws by charging residents significant exit fees without properly disclosing them.
Lifestyle Communities said it relied on legal advice when drafting the contracts, was disappointed with the outcome and intended to appeal.
In health care, Telix Pharmaceuticals was up 6.6 per cent after its prostate cancer imaging agent was granted a permanent insurance code by the US Medicare and Medicaid system.
The Australian dollar was buying 65.20 US cents, from 65.43 US cents at close of business on Tuesday.
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