By early afternoon in New York, the Dow Jones was 1.6pc lower while the Nasdaq had retreated 1.3pc. The S&P 500 had shed 1.1pc.
Some commentators put the declines down to profit-taking after shares rose last Friday – the day of the Supreme Court’s ruling. The spot price of gold advanced 1.8pc to $5,200 as investors gravitated to the traditional safe haven.
Bitcoin, which has singularly failed to mirror gold’s attractiveness amid geopolitical uncertainty, was 4.1pc lower, at $54,744.
It has lost 44pc of its value in the last six months, and 40pc in the past 12 months.
In the US, tech stocks were faring worse as traders returned to the floor after the weekend.
“The market is just experiencing some profit-taking as traders realise that the relief rally from Friday may be premature. You simply can’t bet against Trump.
“He wants tariffs, and he’s going to find a way to implement them,” said Thomas Hayes, chairman at Great Hill Capital.
Shares in Amazon were nearly 2.9pc lower by early afternoon in New York.
Tesla was down 4pc, while Microsoft had fallen 2.4pc. Apple and Nvidia remained in positive territory, however.
Commentary from Nvidia when it releases results tomorrow could offer a key insight about the AI sector that has been hit by growing investor scepticism.
In Ireland, shares were also mixed. By the close, the ISEQ-20 was 0.66pc lower compared to the open.
Decliners include insulation giant Kingspan, which fell 2.3pc to €83.80.
That likely reflected some profit-taking after shares in the company soared more than 8pc last Friday on an upbeat outlook.
AIB was 0.4pc lower, but Bank of Ireland was 0.7pc higher. Permanent TSB was almost 1.6pc lower.
In the UK, the FTSE-100 ended the session flat. Germany’s DAX-40 was just under 1pc lower. France’s CAC-40 was also flat.
German business morale rose slightly more than expected in February, reaching its highest level since August and pointing to the German economy finally turning a corner.
The Ifo institute said yesterday its business climate index rose to 88.6 in February, compared to 87.6 the previous month.
Analysts polled by Reuters had forecast a rise to 88.4.