By all means - "Let's stick with Iraq and the Caliphate".

As to insights into:

1: "whether or not the land-holding group known as ISIS, ISIL, or IS, is indeed evil

For my money it most certainly is, and I would peg that label on any terrorist group who thinks that they can impose their will and their beliefs on any other group of people at gunpoint irrespective of nationality, race, colour or creed.

2: "whether or not it poses a threat to the United States

IS in declaring the establishment of "their" Caliphate have openly threatened the United States, the United Kingdom and other states in the same way that Al-Qaeda did. They have taken hostage foreign nationals and murdered them. The US largely ignored and dismissed threats from such a source before and it learned to bitterly regret it - the same mistake will never be repeated.

3: "whether it's an over-reaction to be planning to bomb their asses

The people to ask about this are those currently and most at risk of suffering under IS "rule" - I do not think for a second that they would say that it is an over-reaction.

In Afghanistan after the Russians had quit the country the Pakistani ISI and Government wanted to put in place an Afghan Government that would do their bidding, an Afghan Government that they could control. Initially their hopes were pinned on Gulbuddin Hekmatyar (Who they had been grooming since 1975) but he proved to be a dead-end. So late in 1994 the Pakistani ISI created "The Taliban" under Mullah Muhammad Omar and set it on its way to take Afghanistan. Opposing the Taliban were the warlords who controlled the various factions of the Mujahideen who had fought the Russians. The Taliban backed to the hilt by the Pakistani Government, Army and Intelligence Services fought that group which came to be known as "The Northern Alliance" for seven years and failed to defeat them. It was this "civil war" that the US and GWB used to drive the Taliban and Al-Qaeda out of Afghanistan and they did it by providing the Northern Alliance with air power, the only "boots-on-the-ground" required were 1,200 Special Advisors - the combination of ~35,000 men from the Northern Alliance, ~65 combat aircraft from two USN Aircraft Carriers and those 1,200 Special Advisors succeeded in running the Taliban and their Al-Qaeda guests out of Afghanistan in 71 days - today the "leadership" of both the Taliban and Al-Qaeda are still hiding out in Pakistani ISI supplied "safe houses" in Pakistan.

As long as the Iraqi Army and the Kurdish Peshmerga forces are supported by US air power and supplied and armed by members of the international community, IS will get nowhere, particularly now that the main Sunni Arab tribes in Iraq are behind the new national "unity" Government. The method is being unveiled in the North of Iraq. Because of the presence of US aircraft IS cannot move (Any time they attempt to do so in any number they get hit) the villages, and towns they occupy are isolated and surrounded, then Iraqi or Peshmerga forces go in. The process is slow but sure. Merely the threat of air strikes inside Syria prevents any serious or effective IS attempt at reinforcement of their troops inside Iraq.


4: "whether or not there will inevitably be a need for 'boots on the ground'

General Dempsey has raised the point that IF he thought it necessary and it became apparent that US ground forces were required for specific operations then he would have no hesitation in recommending that course of action to the President and request the troops required. Personally I do not think such troops will prove necessary.

5: "As for the past, I'm wondering why the Iraqi Army backpedaled so fast when faced with the I S pouring over the border from Syria, why they let so much materiel fall into their hands."

In December 2011 US Forces left Iraq leaving behind it an Iraqi Army that was fairly well trained and competent. Iraqi Prime Minister Nouri Al-Maliki then started meddling with it and replaced many officers and senior commanders with his Shia factions favourites - these were the Iraqi Army Officers and Commanders who ran from IS Forces. That is now no longer a problem, as the Iraqi Army has demonstrated.