The U.S. Travel Association refers to the years 2000-2009 as the "The Lost Decade" of international travel. During those years, the U.S. missed out on approximately 68.3 million visitors and $606 billion. Fast forward to 2016, and those numbers have finally bounced back, with U.S. travel exports growing to 11.2 percent — the highest increase since the fallout from Sept. 11.

However, the U.S. travel industry may be looking at another "lost decade" under President Donald Trump as the White House tightens travel restrictions. A new report shows that Trump's travel ban could cost the U.S. travel industry $18 billion in the next two years.

The report shows that about 4.3 million fewer international travelers will visit the U.S. this year because of the travel bans, equaling to a revenue loss of about $7.4 billion, according to Tourism Economics. The report projects another 6.3 million visitors and $10.8 billion that those visitors would have spent in 2018 will be lost.

On Jan. 27, just a week into his term, Trump signed the first travel executive order, banning entry for 90 days to citizens in seven countries: Iraq, Syria, Iran, Libya, Somalia, Sudan and Yemen.

"We don't want them here," Trump said during the signing of the executive order at the Pentagon. "We want to ensure that we are not admitting into our country the very threats our soldiers are fighting overseas. We only want to admit those into our country who will support our country and love deeply our people."

As protests erupted at airports following the detainment of travelers, those in the travel industry quickly spoke out against the initial travel ban.

"NTA is a firm believer that visa protocols, such as the Visa Waiver Program, are an important part of the nation’s security posture," National Tour Association President Pam Inman said in a statement regarding the executive order. "Certain reforms and restrictions to these protocols have the potential to negatively impact the U.S. economy, and the travel and tourism industry.

"NTA recognizes the administration's right to review visa-issuance protocols with respect to certain countries that may have higher risks of terrorism or lower levels of law-enforcement cooperation with the U.S. government. NTA is counting on the administration to carefully craft any reforms to these protocols to make sure they achieve the desired security benefits."

A day after the initial travel executive order was signed, the ban was blocked by a federal judge in New York.

"There is imminent danger that, absent the stay of removal, there will be substantial and irreparable injury to refugees, visa-holders and other individuals from nations subject to the January 27, 2017, Executive Order,” wrote U.S. federal judge Ann Donnelly in her decision granting the travel ban.

But the damage had been done. Interest in U.S. travel began to drop immediately after the initial travel ban.

According to the Global Business Travel Association (GBTA), the U.S. lost about $185 million in business travel bookings a week after Trump's travel ban went into effect.

"The cloud of uncertainty could leave a lasting economic impact," said GBTA Executive Director Mike McCormick. "Large corporations and small businesses alike will suffer. The biggest driver of our economic recovery of the past seven years from the most recent downturn was international outbound travel."

However, Trump stood by the travel ban in a statement: "America has always been the land of the free and home of the brave. We will keep it free and keep it safe."

Several state courts did not agree with Trump with the route he was taking to keep America safe and blocked parts of the travel ban. The Trump administration appealed to the U.S. Appeals Court, but they too upheld the suspension of the travel ban.

"There is no precedent to support this claimed unreviewability, which runs contrary to the fundamental structure of our constitutional democracy," the 9th U.S. Circuit Court of Appeals said on Feb. 9.

Less than a month after the appeals court upheld the travel ban, a second executive order was signed, revising parts of the initial travel ban. The new executive order still imposes a 90-day ban on travelers of six predominately Muslim countries (Iraq being removed from the new executive order) and also exempts permanent residents and current visa holders.

"Unregulated, unvetted travel is not a universal privilege, especially when national security is at stake," said John F. Kelly, the homeland security secretary during a press conference announcing the updated travel ban.

However the U.S. Travel Association thought differently when the revised travel ban was issued.

"The American travel community supports efforts to bolster national security, and the Trump administration deserves some credit for the substantially more cautious and deliberate introduction of the revised executive order," said President and CEO of the U.S. Travel Association Roger Dow in a statement.

He later added: "Clearly this revised order is very encouraging news if you're looking to come to the U.S. from Iraq. The question remains whether the revised order did enough to mollify the prospective traveler from Canada, Europe or elsewhere around the world who may have been put off by the initial travel ban. If undecided voters need to hear certain things to be motivated to get out and vote, then the same is true for undecided travelers."

The second travel ban has also met the fate as did the initial travel ban with it being blocked by the courts. On March 15, two federal judges (one in Hawaii and one in Maryland) halted the travel ban a day before it was to go into effect.

U.S. District Judge Derrick Watson further extended the ban on March 29. The Trump administration has filed for an appeal extending the blocking of their travel ban.

"These injuries have already occurred and will continue to occur if the executive order is implemented and enforced; the injuries are neither contingent nor speculative," wrote Watson in his judgement.

But many states continue to see the fallout of the ongoing saga of the travel ban, resulting in a drop in the number of international visitors.

New York City is predicting that it will see 300,000 fewer international visitors this year than it did in 2016. That is a 2.1 percent drop. It's the first time the city has seen a drop since 2008.

"These restrictions are creating an image problem for many international travelers, regardless if they're included in the ban or not,'' says Chris Heywood, a spokesman for NYC & Company.

In California, a UCLA study predicts that the "Golden State" may lose about $1.7 billion in spending. While the study credits much of the loss to a strong U.S. dollar, the travel ban could deter even more tourists. The impact of the "friendliness of the U.S." toward foreigners is hard to measure, and to forecast, the report said.

"It may be that it makes the U.S. a more adventurous place to be, but the increased difficulty of getting visas might just do the opposite," wrote Jerry Nickelsburg, a UCLA economist.

A forecast by Tourism Economics for the L.A. County area showed a potential three-year loss of 800,000 international visitors and $736 million in tourism spending.

"All of a sudden there is uncertainty out there," said Lynn Mohrfeld, head of the California Hotel and Lodging Association, which represents about two-thirds of the state's hotels. "If the perception that the U.S. is an unwelcoming destination becomes reality, then it is going to spell a lot of trouble for the travel industry."

To help combat some of the damage the travel ban may have already done, the Los Angeles Tourism and Convention Board is planning a campaign to highlight the area's diversity and show that the region is open to all visitors.

The U.S. travel industry may be on the losing side as potential visitors look elsewhere to visit and the travel industry plunges to uncertainty.

"We're hearing concern," Dow said. "Our message to the Trump administration is real simple: 'We’re real good at America being closed for terrorism and open for business.' What we need them to do is say that."