President Trump plunged the United States even deeper into a series of costly global conflicts this week, creating new economic hazards that have rattled financial markets, risked another rise in prices and unnerved some Republicans ahead of the 2026 election. On a day when Mr. Trump was set to rally G.O.P. voters ahead of the approaching midterms, the consequences of the president’s agenda were on full display. A trade war he initiated with Canada appeared headed toward another escalation, while a new outbreak of fighting in Iran sent oil prices above $100 per barrel for the first time since July.

Both developments threatened to unleash even higher costs on American families and businesses, which have already been stung by years of unchecked inflation that Mr. Trump has pledged to tame. The president’s attacks on Canada — and his new bid this week to block some of its exports to the United States altogether — risked damage to American states and domestic industries that rely heavily on commerce across the border. The average cost of a gallon of gas topped $4.22 nationally on Wednesday.

The fallout has complicated Mr. Trump’s task to convince a restive electorate that the nation is on the right track. While the economy once might have served as Mr. Trump’s source of political strength, it has recently become his greatest liability, jeopardizing Republicans’ hold on Congress. Senator Susan Collins of Maine voiced objections, pushing to relax duties on road salt and other products. The mounting uncertainty sent major indexes lower, and government bond yields rose, affecting mortgage costs for consumers.

Despite his efforts, majorities of voters increasingly tell pollsters they blame the president for their financial troubles. At the midterm convention in Texas, he plans to reprise his message that his policies have grown the economy and driven down prices.