(CNN)A combination of Iraqi forces has converged on Ramadi in an effort to reverse ISIS' stunning success in seizing the city.

The Iraqi Prime Minister, Haider al Abadi, promised a counter-attack "within days" as Baghdad seeks to address the most humiliating episode in its war with ISIS since the fall of Mosul nearly a year ago.

ISIS -- in both Iraq and Syria -- has had a successful month. Its capture of Ramadi and Palmyra in Syria are due to its tactics and structure, and the weakness or exhaustion of opponents, as well as support or acquiescence among enough Sunnis in both countries. It may also have benefited, according to some analysts, from cynical power-plays in Baghdad.

Even so, taking Ramadi and holding it are two different things. Evidence from previous battles suggests that ISIS doesn't 'do' defense as well as offense, and it is still vastly outnumbered by Iraqi forces. But the longer ISIS fighters are entrenched anywhere the more difficult they are to expel, and the Iraqi Security Forces (ISF) clearly aren't capable of the task alone.
Good read on the situation.