This week's terrorist attack, which killed eight people and injured about dozen others in New York City, horrified the country. But it likely did not shock Acting Homeland Security Secretary Elaine Duke.
Just two weeks earlier, Duke warned in a speech in London that such "small plots" would pick up in the United States and other Western countries as the Islamic State loses territory in the Middle East.
"Terrorists are strong, they are adaptable, and the terrorist threat is the highest it has been since pre-9/11," she said at the U.S. embassy, according to the Daily Mail. "We have got to have every tool that's possible."
More chillingly, Duke predicted that ISIS would use the attacks as a means to keep a high profile and raise money as prelude to a large-scale attack along the lines of the 2001 attacks that destroyed the World Trade Center in New York and damaged the Pentagon.
Federal prosecutors have charged Sayfullo Saipov, a 29-year-old from Uzbekistan, who came to the United States in 2010 under the Diversity Immigrant Visa Program.
Terrorism expert Steve Emerson said Duke is right.
"I think she's demonstrated the fact that there's going to be an expansion of these attacks," he said.
U.S. counterterrorism officials have had remarkable success detecting and stopping terrorism plots since 9/11. But stopping the kind of attack launched Tuesday — a low-tech plot involving a rented pickup truck that mowed down pedestrians on a bike path — is the hardest to stop.
Emerson, executive director of The Investigative Project on Terrorism, said it requires vigilance and a willingness by law enforcement authorities to monitor radical mosques and people associated with them. He faulted New York City Mayor Bill de Blasio for dismantling a police initiative that took such actions.
He also criticized former President Barack Obama's administration for imposing a 60 percent cut in funding for a program that trains terrorism informants and for shutting down working groups at the FBI field office in Washington that focused on specific terrorist organizations.
Emerson also challenged the explanation that Saipov became "self-radicalized." He pointed to reports that Saipov left notes in Arabic in the pickup truck. He said that is an indication that he may have been influenced by a radical mosque in the United States or, perhaps, the Middle East.
"The notes that he left in the truck were Arabic, all handwritten," he said. "Arabic and Uzbek are totally different languages, not easy to master."
Emerson said counterterrorism authorities need to search for signs of such radicalization.
"This guy didn't get radicalized over one year because he got ISIS videos," he said. "This is a process that began probably before he got here."