Speaking at the Center for Strategic and International Studies on Monday, CIA Director John Brennan stated that the Islamic State had been "decimated" during George Bush’s presidential tenure.
"[ISIS] was, you know, pretty much decimated when U.S. forces were there in Iraq," said Brennan. "It had maybe 700-or-so adherents left. And then it grew quite a bit in the last several years, when it split then from al-Qaeda in Syria, and set up its own organization."
In 2014, however, ISIS could muster "between 20,000 and 31,500 fighters across Iraq and Syria," according to a CIA report.
Estimates vary widely, with some currently placing the number of ISIS fighters at 50,000, and others at 200,000. Daveed Gartenstein-Ross of the Foundation for Defense of Democracies think the number is closer to 100,000 than 30,000.
Using the CIA’s own numbers, this is an increase of fighters ranging from 2,700% to 4,400% during President Barack Obama’s tenure. Using higher estimates other than the CIA’s — 50,000 and 100,000 — the range of increase is between 14,000% and 28,000%.