Most foreign-born terrorists radicalized 'years' after coming to US, DHS report Report aimed at informing law enforcement on homeland terror threats.

 -- Most foreign-born terrorists operating in the United States were radicalized "several years" after entering the country, according to a recently published Department of Homeland Security intelligence assessment.

The findings may undercut the ability of officials to prevent their entry to the U.S. through the vetting and screening process as well as the counterterrorism argument behind President Donald Trump's travel ban, which is being held up by court order.

The report -- first reported on MSNBC's "The Rachel Maddow Show" and independently obtained, reviewed and verified by ABC News -- is consistent with previous non-governmental data and analysis that has been released over that past few years.

A DHS spokesperson confirmed the authenticity of the unclassified, internal report, calling it an "official DHS assessment" used to inform federal, state and local partners on the "trends of foreign-born individuals engaged in terrorism activity in the Homeland."

Homeland Security downplayed the significance of the report, pointing out that the information was derived only from "unclassified, open source materials" and does not include information from "historical or current investigative case data" or "current intelligence from classified data."

It was published internally on March 1, 2017 and was coordinated with numerous agencies, including the Department of State, Immigration and Customs Enforcement (ICE) and Customs and Border Protection (CBP).

According to John Cohen, an ABC News contributor and former acting undersecretary for intelligence at DHS, if the report was inconsistent with current intelligence reporting it would have been resolved in clearance process before it was published.

The government-produced assessment comes at a time when the Trump administration is expected to unveil a revised immigration executive order.

Trump’s previous order, which temporarily banned travel to the U.S. by immigrants from seven majority-Muslim countries, as well as a temporary ban on all refugees, was halted by a federal court judge in Washington state on Feb. 3. . An appeals court denied the Trump’s request to reinstate the order.

"I’m establishing new vetting measures to keep radical Islamic terrorists out of the United States of America. We don’t want them here," Trump said at the signing of the original order on Jan. 27. "We only want to admit those into our country who will support our country and love deeply our people."

According to Cohen, the report "undermines" the reasoning behind Trump's ban because terrorist attacks are primarily carried out by people already in the U.S., not those coming from overseas.

"This intelligence assessment absolutely undermines the justification for the proposed travel ban," said Cohen.

The findings are constant with past reports and studies on this issue, like the George Washington University program on extremism, which found that the "vast majority" ISIS attacks in the U.S. were carried out by U.S. citizens or permanent residents.

Last year, then-Homeland Security Director Jeh Johnson said in Congressional testimony that the terror landscape had shifted from terrorist-directed attacks, to a world that also includes the threat of "terrorist-inspired attacks – attacks by those who live among us in the homeland and self-radicalize, inspired by terrorist propaganda on the internet."

"By their nature, terrorist-inspired attacks are often difficult to detect by our intelligence and law enforcement communities," he added.

By focusing on banning people from certain countries, rather than the psychological and behavior characteristics that draw people to radicalization, authorities could miss the "key threat," said Cohen.

The DHS office of Intelligence and Analysis, which released the report, based its findings on the examination of 88 people, who either conducted or planned attacks in the U.S., provided funds to overseas terrorist organizations or traveled to join a terrorist group.

The report also found that nearly half of the foreign-born, U.S.-based violent extremists examined were less than 16 years old when they entered the country.

The majority of those lived in the U.S. for more than 10 years before they were either killed or were charged.

For example, the report cites, a man from Bangladesh who came to the U.S. when he was 11-months-old and lived in the country for 24 years before travelling to Syria and joining ISIS, as a well as Cuban man who came to the U.S. in 1989, but didn't start displaying signs of radicalization until 2015.

A previous DHS study found that of the most recent cases, between Jan. 2015 and Dec. 2016, these extremists began radicalizing on average 13 years after coming to the U.S., according to this report.

Justin Fishel contributed to this report.