by Matthew Rusling

WASHINGTON, Sept. 11 (Xinhua) -- Terrorism is still a threat to the United States, even 17 years after terrorists killed nearly 3,000 civilians in the Sept. 11, 2001 attack on New York and Washington, U.S. experts said.

Tuesday marked the 17th anniversary of a day that shocked the world, when members of terror group al-Qaeda hijacked four airplanes, slamming three of them into New York and Washington, in a day that will live in infamy. As memorial services went on throughout the nation to mourn the victims, experts said the terror threat continues.

"Terrorism remains a threat to the U.S. and Americans," Wayne White, former deputy director of the State Department's Middle East Intelligence Office, told Xinhua.

That's because "terrorists already part of American society (are) being radicalized in place by ideologies planted by al-Qaeda and ISIS," White said of the two most dangerous terror groups.

Brookings Institution Senior Fellow Darrell West echoed those sentiments, telling Xinhua, "It has been 17 years since the 9/11 attack but the fear generated by that attack continues to affect U.S. policy making. The country has invested billions in counter-terrorism but the threat remains."

Dan Mahaffee, senior vice president and director of policy at the Center for the Study of Congress and the Presidency, also echoed those thoughts.

"In the anniversary of 9/11 we are reminded that terror remains a threat around the world, not just to the United States," he told Xinhua.

"While policies aimed at fighting ISIS are showing promise, there continues to be the threat of homegrown terror and plots inspired from abroad," Mahaffee said.

Robin Simcox, Margaret Thatcher Fellow at the Heritage Foundation, told Xinhua that Islamist ideology has spread across the globe in the years after 9/11.

"America remains the country that terrorist organizations aspire to attack more than any other. Of the most dangerous terrorist organizations, ISIS has lost the majority of its territory in Iraq and Syria, but remains a potent threat, with affiliates dotted across the Middle East and Africa. Al-Qaeda, meanwhile, has a significant presence in Syria, Yemen and Somalia -- among other countries -- and still retains a clear desire to attack the U.S.," Simcox said.

"The U.S. also has to defend itself against those such as Pulse nightclub gunman Omar Mateen, who was radicalized domestically," Simcox said, referring to the 2016 extremist attack on a gay nightclub in Orlando, Florida, which killed about 50 people.

"This type of danger is arguably the most pressing issue that U.S. law enforcement faces from Islamist terrorists today," Simcox said.

TRUMP AND TERRORISM

Simcox said the Trump administration has "correctly" prioritized breaking ISIS' territorial grip in Iraq and Syria, while drone strikes against dangerous al-Qaeda franchises such as that in Yemen have significantly increased.

However, there is always more that needs to be done in the fight against Islamist terror groups. For example, ISIS will look to make a comeback and ultimately aspires to govern once again. "The administration must actively prepare itself for this eventuality," Simcox said.

Critics say that Trump seems to have put the terror threat on the back burner since being elected nearly two years ago.

"Trump has shown little real interest in Syria, Iraq, ISIS, al-Qaeda or Afghanistan since being elected," White said.

The president has "taken several anti-Palestinian actions in the Israeli-Palestinian arena that could radicalize not only Palestinians, but other Arabs and Muslims inside and outside the U.S.," White said.

Indeed, the U.S. president last year recognized the city of Jerusalem as Israel's capital, a critically important city that both Judaism and Islam claim as holy site, and Trump's doing so has sent the message that Washington is far from neutral, and is siding with the Israelis.

"Trump also has angered allies needed to cooperate against terrorist plots, and made the U.S. less popular abroad, neither of which contributes to U.S. security," White continued.

Moreover, the U.S. Muslim community feels singled out for scrutiny, as Trump has made a number of comments that Muslims feel unfairly targeted them.

"Any nation's policies that single out specific religious or ethnic groups raise the risk of worsening the threat of terror from isolated communities or isolated segments of society," Mahaffee said.

THE NEXT ATTACK

Still, experts agree that another spectacle like the 9/11 attacks is unlikely. While the U.S. got caught sleeping at the wheel in the lead up to the attack, it's unlikely to happen again.

While 2013 saw the Boston Marathon Bombing -- a home made bomb set off by two extremists living in the U.S. that killed three people and injured several hundred others -- future attacks are likely to be smaller.

Examples could include mass shootings in which the perpetrator opens fire on a crowd -- such as the 2016 attack on a gay nightclub in the U.S. state of Florida, carried out by radical Muslim Omar Mateen, a 29-year-old civilian living in the U.S. Other scenarios might include a van or truck driving at top speeds in an urban area and crashing into crowds, such as the 2017 London bridge attack in England.

"Another grand 9/11-like plot is unlikely because most extremists seem to realize organizing such a sweeping plot is more susceptible to detection," White said.

"The most likely scenarios are continued American casualties from individuals or small groups already present in the U.S. -- radicalized in place -- as well as a stream of U.S. casualties -- mostly military -- from involvement in places from Afghanistan to Niger," White said.