The Pentagon warned on Thursday the Islamic State is “well-positioned to rebuild and work on enabling its physical caliphate to re-emerge.”

“ISIS probably is still more capable than al-Qaida in Iraq at its peak in 2006-2007, when the group had declared an Islamic State and operated under the name Islamic State of Iraq,” Pentagon spokesman Cmdr. Sean Robertson told Voice of America News in an email.

“ISIS remains a threat, and even one ISIS fighter is one too many,” Robertson said.

The Pentagon was responding to questions about a Defense Department estimate of between 28,000 and 32,000 ISIS fighters active in Iraq and Syria, which is not far from the numbers fielded by the terrorist gang when it ruled a “caliphate” stitched together from conquered territory in Syria and Iraq. Voice of America noted the United Nations made a comparable estimate of Islamic State troop strength.

These estimates are controversial in the Defense Department because some officials believe the raw total of active ISIS fighters greatly overstates the actual strength of the terrorist organization. Those numbers are thought to include a fair number of noncombatants such as family members and ISIS supporters unwilling to fight for the organization.

“Yes, there are still residual numbers of ISIS members, but manpower is not a good metric to assess the volatility of this terror group,” Robertson said.

If there really are 30,000 fighters still active in Iraq and Syria, it would mean ISIS has returned to its original troop strength after suffering nearly 70,000 casualties, in part by recalling Islamic State fighters from operations in other countries. Most intelligence profiles of ISIS portray the group as doing the opposite, sending fighters from the collapsing Syria-Iraq caliphate to other countries where Islamic State leaders believe they have a better chance to survive.

Another troubling detail provided by the U.N. estimate of ISIS strength said, “Its financial reserves have declined but not dried up.”

Thanks to income from extortion, kidnapping, and oil resources it still controls, the Islamic State is believed to have a treasury “in the low hundreds of millions of United States dollars,” according to the United Nations.

A report at NATO Review last week suggested that imprisoned ISIS members are “mostly low-level fighters who surrendered or were taken alive,” leaving a small number of survivors on the loose who are “potentially very dangerous” because they were the cream of the Islamic State’s recruits, frequently boasting professional military training from their country of origin.

Another disturbing hypothesis from NATO Review is that some of the survivors were ultra-hardcore militants who thought the leadership of the Islamic State was too soft and correctly judged it was making mistakes that would lead to the destruction of the caliphate. Some of this group bribed their way to safety and took large amounts of Islamic State money with them. Others managed to evade the U.S. coalition, the Syrian regime, rival terrorist gangs like al-Qaeda’s Nusra Front, and brutal purges by ISIS leadership, making them incredibly dangerous individuals.

In this analysis, the fall of the caliphate weeded out the weakest members of the Islamic State and left the most cunning fanatics on the loose, ready and willing to reconstitute the terrorist organization. Not only are these ISIS survivors able to spread the group’s poisonous ideology and recruit new members, but they have a reasonable expectation that waves of imprisoned low-level Islamic State veterans will be released over the next few years, making it possible to replenish their manpower with a little patience.