How big of a threat is ISIS really?
The White House wants to find out and is deploying as many as 300 military advisers to Iraq to assess the might of the Islamic State in Iraq and Syria.
The jihad group's rash battlefield successes make them look extremely fierce.
They have surged over from northern Syria to blitz major cities in Iraq's Sunni region, taking Tal Afar and Mosul then moving quickly south. Hundreds of thousands of civilians fled from their path, creating a new refugee crisis.
They have advanced on Baquba, just north of Baghdad and are threatening to attack the capital.
The Obama administration has said there will be no more American boots on the ground after the drawdown of all American troops - tens of thousands of them.
It's up to the advisors to help Iraqi security forces vanquish ISIS on their own.
Washington has said little about what they'll actually be doing - and expert opinions on that and on whether they should be in Iraq at all are split.
Who are they?
They are high-ranking officers. They are Navy SEALs and Army Rangers, said retired Marine Sgt. Adam Banotai.
Banotai, who scrapped through the brutal battle for Fallujah during the Iraq war, thinks the term 'adviser' is misplaced.
"It is political semantics," he said. "We are calling them adviser now...instead of combat troops or boots on the ground." said retired Sgt. Adam Banotai.
"They are the most elite fighters we have," he added. "So, if they aren't going to be combat troops - I'm not quite sure who the president is going to refer to as combat troops."
MORE on CNN.com