In May, traffic from Canada on the home listing site fell by 26.4 percent from the same time a year ago, marking the fourth straight month of double-digit year over year declines in searches for homes in the United States. The pattern follows President Trump’s announcements to enact, pause and negotiate tariffs on the country. While there was a dip in overall traffic to the site during the same period, it was dwarfed by the drop from Canada, said Chen Zhao, the head of economics research for Redfin.

The first major plunge happened in February, when searches from Canada declined by 21.3 percent year over year — a marked shift from January, when searches were down just 3.6 percent from the prior year.

“This is a big earthquake,” Dr. Zhao said. “You just don’t see that happen.”

In 2024, Canadians accounted for 13 percent of all foreign buyers in the United States, more than any other nation, spending $5.9 billion on American real estate, according to the National Association of Realtors. Half of Canadian buyers purchase vacation homes, usually in warm-weather areas, favoring Florida, followed by Arizona, Hawaii and California, according to N.A.R.

“If the Canadian buyers aren’t coming to spend their winters in Florida or Palm Springs, then they are also not spending their money there, and that has implications for the local economy,” said Dr. Zhao.

The collapse in activity from Canadian buyers follows the timeline of Mr. Trump’s trade policies, which began Feb. 1, when he announced 25 percent tariffs against Canada and Mexico. As a trade war ensued, he repeatedly suggested that Canada should become the 51st state. In turn, Canada levied reciprocal tariffs and elected a new prime minister, Mark Carney, who described the tariffs as “the greatest crisis of our lifetimes.”

About a year ago, another of Mr. Kastanis’s Canadian clients bought a three-bedroom condo in Coconut Grove. But now, with the prospect of tariffs, he needs to spend less time at the beach enjoying a partial retirement and more time tending to his construction business back home. “He didn’t plan for his Miami exit,” said Mr. Kastanis, who is listing the condo for $4 million.

Since the tariffs went into effect, Marc Rasmussen, an agent with Corcoran in Sarasota, Fla., has also seen a drop in interest from Canadian buyers, with some clients pausing their searches and others telling him they are no longer interested in American real estate. One of his clients, a married couple, could not sell their two-bedroom condo in Siesta Key for almost a year. It was originally listed for $699,000. Once the trade war started, they got anxious and more flexible in their pricing.

“They didn’t know what the heck was going to happen,” Mr. Rasmussen said. Before long, they’d accepted an offer of $520,000.

Some of his buyers have stopped looking, uncertain of a changing economic climate. “We had some people say, ‘Absolutely no, we’re not going to buy there,’” Mr. Rasmussen said. “And then we have some people say, ‘We’re just going to wait and see how this plays out.’”