President Donald Trump defended his plan to ban immigrants from terror-prone countries by arguing that the FBI’s terror investigations are at an all-time high due to policies of the previous administration.

"President Obama and Hillary Clinton have, and (former Secretary of State John) Kerry have allowed tens of thousands of people into our country," Trump said on ABC News Jan. 25. "The FBI is now investigating more people than ever before having to do with terror. And it's from the group of people that came in. So look, look, our country has a lot of problems. Believe me. I know what the problems are even better than you do. They're deep problems, they're serious problems. We don't need more."

We couldn’t independently verify the number of current FBI investigations and compare that to the past, and Trump put no timeframe on his historical comparison. We decided not to put Trump’s claim on the Truth-O-Meter, but we will lay out the evidence we found from experts. A spokesman for Trump did not provide any information to back up the claim by deadline.

Experts told us that the number of investigations alone doesn’t provide a complete picture about the scope of terrorism in the United States.

"Just because someone is being investigated for terrorism does not mean that the terrorism threat is up," said Laura Dugan, a University of Maryland professor of criminology and criminal justice. "It just means that the FBI is increasing investigations."

FBI investigated about 1,000 cases last year

A spokesman for the FBI told us that the agency doesn’t release information about the number of terrorist investigations under way, but pointed to statements by director James Comey that the FBI has investigations in all 50 states.

Multiple news reports paraphrased Comey as telling reporters at a May 11, 2016, news conference that the FBI has investigated about 1,000 cases — up from 900 the year before — to determine if a suspect is consuming terrorist propaganda, or acting on it. Trump cited the 1,000-case figure on Fox News on Jan. 26, a day after his ABC interview.

Comey’s comments coincided with the opening of a trial in Minneapolis of three Somali-Americans accused of plotting to help the Islamic State.

The New York Times wrote in September 2016 that in recent years the FBI has "averaged 10,000 assessments annually, and 7,000 to 10,000 preliminary or full investigations involving international terrorism. In addition, the FBI receives tens of thousands of terrorism tips."

We sought data on charges or convictions from the U.S. Justice Department but did not get a response.

Databases show many terrorists in the United States are Americans

Trump suggested that the people suspected of being terrorists are immigrants or refugees brought in under the Obama administration’s policies. His team did not present evidence backing up that assertion, and checking out who is under FBI investigation is, of course, difficult.

Data suggests that many of these cases were committed by citizens or legal residents. It is tricky to quantify what percent of terrorists are immigrants vs. Americans because the definitions of terrorism vary -- even among federal agencies. Right-wing terrorism can be motivated by attacks on the American political system, which is different from terrorism linked to al-Qaida.

While there have been high-profile incidents involving legal immigrants, databases of terrorist acts show many were homegrown extremists.

According to the New America Foundation, about 81 percent of individuals accused of jihadist terrorism crimes since Sept. 11 are citizens or legal residents and about 48 percent were born with U.S. citizenship.

In terms of overall figures, the foundation reported that 2015 was the peak year with 79 cases of people charged with jihadist terrorism related crimes or having died before a charge. That number dropped to 43 in 2016, although that number could grow if additional cases are unsealed, said David Sterman, New America policy analyst.

The foundation draws from court records, government press releases, and news reports. The New America database includes cases that involve a terrorism charge or could be considered terrorism even if the charge is something else, for example the Fort Hood case where the charges are murder.

A New York Times analysis in 2015 found that half of the jihadist attacks since 2001 were committed by men born in the United States. Many others were naturalized citizens.

Other databases show some information related to tracking terrorism but didn’t reflect the full number of FBI investigations.

George Washington University collects data on the number of individuals charged with offenses related to the Islamic State. There were 61 individuals in 2015 and 33 individuals in 2016 charged with ISIS-related activity. The university reported that the vast majority were Americans.

Numbers don’t tell the full story

The number of cases can rise if the FBI decides to make suspected terrorists more of a priority — but that doesn’t necessarily mean there is more terrorism. Also, not all terrorism cases carry the same level of threat. A charge against someone for material support is not the same as charging someone accused of carrying out an attack. Also, only some investigations lead to actual charges and then convictions.

American University professor Tricia Bacon, who worked in counterrorism for the State Department from 2003-13, said that only FBI headquarters could credibly measure whether the FBI is investigating more people than ever before for terrorism and why.

John Mueller, an adjunct political science professor at Ohio State University and senior fellow at the libertarian Cato Institute, said that the FBI has followed up on millions of terrorism leads since Sept. 11, 2001.

"Although scarcely any develop into anything, the FBI continues and is probably getting more efficient at it, made more so by the fact that so many would-be terrorists announce their intentions (or fantasies) on Facebook and Twitter," he said.

Max Abrahms, assistant professor of political science at Northeastern University, said he wouldn’t be surprised if the number of people under investigation by the FBI for terrorism is unprecedented. However, he noted some problems with attempting to ban people from certain countries.

"No nation has a monopoly on terrorists," he said. "And no nation is exempt from producing them. Furthermore, the ban does not affect domestic terrorism, which is a growing concern, by not only Islamists, but also right-wing extremists."

Our conclusions

Trump said "The FBI is now investigating more people than ever before having to do with terror."

We did not find any definitive data to show whether the FBI is currently investigating more people for terrorism than any point in the past. Comey said in May that the FBI has investigated about 1,000 cases -- up from 900 a year or so ago.

The New America Foundation reported that 2015 was the peak year for cases of people charged with jihadist terrorism related crimes or having died before a charge but being credibly reported to have engaged in jihadist terrorism.

However, experts told us that the numbers alone don’t tell the full story because it doesn’t show how many result in actual convictions and not all cases have the same level of seriousness.

"Large numbers of investigations or prosecutions are a worrisome indicator of threat, but there are other indicators including the sophistication of plots, the direction of the trend line in cases, and whether plots are being detected early or late in the plotting process that must also be considered," Sterman said.