One day after House Republicans approved an expensive package of tax cuts that rattled financial markets, President Trump pivoted back to his other signature policy priority, unveiling a battery of tariff threats that further spooked investors and raised the prospects of higher prices on American consumers.

For a president who has fashioned himself as a shrewd steward of the economy, the decision to escalate his global trade war on Friday appeared curious and costly. It capped off a week that saw Mr. Trump ignore repeated warnings that his agenda could worsen the nation’s debt, harm many of his own voters, hurt the finances of low-income families and contribute far less in growth than the White House contends.

The tepid market response to the president’s economic policy approach did little to sway Mr. Trump, who chose on Friday to revive the uncertainty that has kept businesses and consumers on edge. The president threatened 50 percent tariffs on the European Union, and a 25 percent tariff on Apple. Other tech companies, he said, could face the same rate.

Since taking office, Mr. Trump has raced to enact his economic vision, aiming to pair generous tax cuts with sweeping deregulation that he says will expand America’s economy. He has fashioned his steep, worldwide tariffs as a political cudgel that will raise money, encourage more domestic manufacturing and improve U.S. trade relationships.

But for many of his signature policies to succeed, Mr. Trump will have to prove investors wrong, particularly those who lend money to the government by buying its debt.

So far, bond markets are not buying his approach. Where Mr. Trump sees a “golden age" of growth, investors see an agenda that comes with more debt, higher borrowing costs, inflation and an economic slowdown. Investors who once viewed government debt as a relatively risk-free investment are now demanding that the United States pay much more to those who lend America money.