Image copyright DANIEL SLIM

Travel experts began warning even before the 2016 election that Donald Trump's campaign rhetoric could cause a decline in tourism. So has the so-called "Trump slump" arrived?

Stephen Mumford, a professor of metaphysics at Durham University in north-east England, had some money to burn thanks to a large research fellowship grant he was awarded in October 2016. Always eager to travel to other countries and present his research, he began making arrangements for trips to several academic conferences in the United States.

Then Donald Trump won the November 2016 election.

In his first month in office, the Trump administration imposed a travel ban on seven majority-Muslim countries, and empowered US Customs and Border Protection agents to enforce immigration laws more assertively at ports of entry.

Media playback is unsupported on your device Media caption Protesters gather at Dulles airport: "Welcome to the USA!"

Mumford started to hear stories he didn't like - like the British Muslim school teacher who was separated from his students and removed from a flight bound for the US, or that incoming travellers were being asked to turn over their mobile phones and social media passwords.

Last month, Mumford made what he says was a difficult decision: to cancel all his planned travel to the US.

"I don't want to go to a conference if other people are excluded simply because they belong to a particular group," he says.

"I don't feel I can just walk in and think, 'I'm OK', and forget the guy behind me can't come in just because he's a Muslim. That's being a party to the unfairness."

Image copyright Joe Raedle

Mumford is not alone.

Thousands of professors around the globe have pledged not to travel to the US.

A growing list of Canadian schools who once made regular trips across the border for sports, music and other educational events are cancelling their journeys for fear that foreign-born students could be singled out.

In Philadelphia, at least one large conference worth an estimated $7m in revenue to the city has been cancelled, and the tourism board of New York City recently reversed its pre-election projection that the city would see an increase of 400,000 international travellers in 2017.

The board now predicts 300,000 fewer foreign tourists will visit the Big Apple this year than did in 2016.

Anecdotes like these are the worst fears of travel industry analysts, who've been warning for weeks that the US could be entering a tourism "Trump slump".

The online booking site Kayak reported that searches by UK citizens for US destinations had "fallen off a cliff", and that hotel prices in cities like San Francisco, New York and Las Vegas dropped between 32-39%.

Hopper, another travel site, released data showing that searches for flights to America had dropped globally an average of 22%.

By contrast, the online travel agent site Tripsta reported a spike in one-way flights from the UK to the US in January and February of 2017, but hypothesised the cause could be "the return of non-US nationals concerned about restrictions to international travel".

The Global Business Travel Association estimated that for the week Trump's travel ban was in effect, the US lost $185m in travel bookings (£150m).

Image copyright JOSHUA LOTT Image caption A Syrian refugee family who was previously banned by Trump's executive order celebrate their entry into the US

But the president can't shoulder all the blame.

Adam Sacks, president of Tourism Economics, characterises the slowing of tourism interest as a "trifecta of travel hindrances": a weak global economy, a strong US dollar and the "falling favourability" of the US in the eyes of the international community.

International travel was already down in 2016 by about 0.9% compared to 2015. Travel to the US from Canada was down 1.4% in December 2016 compared to the previous month, but overall, 2016 was the third consecutive year that fewer Canadians went to the States.

"We expected 2017 to be a fairly subpar year in any case - very modest growth," he says. "[But] this couldn't come at a worse time.

"The US is an expensive destination, we have a muted global economy and now we pile this on - that's why the impacts are as significant as they are."

His firm projects a loss of 6.3 million visitors by next year, which translates into $10.8bn in lost revenue, including what Sacks calls "Trump-induced" losses.

Henry Harteveldt, an analyst with the Atmosphere Research Group, says the US tourism industry has probably already bounced back from the immediate impact of the blocked travel ban. However, industry insiders are anxiously awaiting the language of the new executive order to replace it.

"There are a lot of unknowns. The travel industry, which is already a discretionary industry, hates uncertainty," he says.

Media playback is unsupported on your device Media caption Iraqi Fuad Suleman, who was turned back in Cairo, says he and his family had been preparing to emigrate to the US for two years

Harteveldt points to a survey his firm conducted weeks before the executive order took place, which showed that in 15 countries around the world about 20% of the respondents reported that as a result of the presidential election they were either somewhat or highly unlikely to travel to the US or had actually cancelled a planned trip.

"The fact that in 15 countries so many people had either cancelled trips or had such an unfavourable view of the United States was really alarming to me as an analyst," he says.

"Events that transpired during the presidential election just created a very bad impression of the US in many people's minds."

Image copyright Jack Taylor Image caption Trump's travel ban inspired protests around the globe, including this one in London

Lori, a mother of two boys in Edmonton, Alberta, says they used to make regular trips to the Twin Cities in Minnesota. After Trump's executive orders on immigration, her sons urged her to cancel a trip in March.

"For our oldest, it was out of outrage: the majority of his friends are either visible minority immigrants/refugees, or the children of immigrants or refugees; some of them are Muslim," she wrote in an email.

"For our 11 year old, it was fear: he equates the word 'America' with violence and discrimination against innocent people now."

Although some of the frenzy over President Trump may cool in the coming months, Sacks says that international travellers are booking their spring and summer holidays now.

"This is a massive negative economic impact that's at stake here. It will result in appreciable declines in tax revenues, and will affect household income and also employment and profitability for the industry," he says.

"It will hurt."

How much it will hurt will be more apparent later, once the high travel seasons of spring and summer arrive, and after publicly held airlines, hotels and travel agencies file their earnings reports in mid-April.

The US government also has not yet released this year's visa-entry figures, which will also reveal more about how travel has been affected.

Mumford says that though his decision not to attend a prestigious conference in California could hurt him professionally, he can't put aside his unease over the changes he sees happening in the US.

"I've got the travel money, and if I'm not wanted or regarded suspiciously, then I'll go elsewhere," he says.

"I feel I'm showing solidarity with my friends in America by this minor protest."