The US could be on the verge of a tourism shock. Interest in traveling to the US from at least 94 countries has fallen sharply since Donald J. Trump was sworn in as president, according to Hopper, a digital travel agency.

Overall average interest in flying to the US declined 17% from the three weeks before Trump’s inauguration to two weeks afterward, Hopper said, based on weekly averages of an analysis of billions of global flight searches. Trump signed an executive order temporarily banning residents of seven Muslim-majority countries a week after he was inaugurated.

Last year during the same period, interest in flying to the US fell 1.8%, suggesting that the recent downturn is much more than just a seasonal fluctuation.

Flight searches are an indication of interest in future tourism. So before a decline of tourists is seen at landmarks, museums, or restaurants, it can be observed in the behaviors of would-be tourists as they research and book travel.

International tourism’s value to the economy is also calculated as an export, so any reduction in tourists from overseas could also exacerbate the US’s trade deficit—exactly the opposite of Trump’s stated policy goals.

Hopper compared the number of searches it received for travel to the US in the weeks before the inauguration (when Trump’s exact policies were still unknown) to the week after he signed an executive order barring US entry to nationals from seven countries, and which made the visa process more cumbersome for others.

The US city slated to miss out most is San Francisco, whose airport saw a 33% decline in international interest, Hopper said. Seven other US airports saw a 20% or more decline in search interest over the three week period.

For the seven countries covered by the travel ban, search for travel to the US is down 33%, although Hopper receives no data for Yemen and little data for Somalia, Syria, and Libya.

On the other hand, there was a huge increase in interest in travel to the US from Russia. Flight searches from Russia to the US rose 88%, Hopper said.