The Threatening Storm: The Case for Invading Iraq, is a book that was written in 2002 by former CIA and Clinton Administration official Kenneth Pollack. In it, Pollack argues that the U.S. is overwhelmingly likely to face military conflict with Iraq eventually, and thus it ought to invade now so as to minimize the damage to both sides. A lot of people believe that The Threatening Storm makes the best argument out there for invading Iraq; a much better case, in fact, than that being made by the Bush Administration.

Pollack begins his case by recounting the rise of Saddam Hussein in Iraq, and moves on to more recent events, including the Iran-Iraq war and Iraq's invasion of Kuwait. He then describes the history of the current sanctions/inspections regime, before presenting an analysis of the current state of affairs.

Pollack identifies four basic policy options for the U.S. First, containment: essentially, continuing the current sanctions and inspections regime. Second, deterrence: dropping the sanctions, discontinuing inspections, and relying on Saddam's self-interest to keep him from doing anything stupid/launching an attack. Third, the "Afghanistan" approach to Iraq, wherein the U.S. would provide support for an indigenous army, who would overthrow Saddam with American assistance. Fourth, a full-blown invasion, occupation, and post-WWII-style Japan (or Marshall Plan)-ish rebuilding of the country.

For a full treatment of each of these, really, read the book. But to summarize, Pollack believes that:
(A) Containment is failing and will continue to fail, creates the perception that the U.S. is intentionally exacerbating Iraqi suffering, and is in any case incapable of permanently removing the threat Saddam Hussein presents;
(B) Deterrence isn't realistic, since Saddam has a history of risky, incorrect decision-making, has shown in the past (igniting the Kuwaiti oil fields, attemtping to assassinate Bush I, etc.) that deterrence often fails with him, and is likely to eventually get nuclear weapons not to use directly against the U.S. but rather to use as a deterrent against U.S. intervention against his aims (political and military) in the Middle East;
(C) There is no indigenous Iraqi force capable of effectively overthrowing Saddam's regime; and
(D) Invasion is essentially the least-bad option, since the risk of a nuclear-armed Saddam outweighs the risk of an invasion at this point.

(I can't stress enough how inadequate these summaries are. Pollack's examination of each option and its likely consequences is much more complete.)

It's worth mentioning that despite favoring invasion, Pollack explicitly rejects a few key assertions of most Iraq hawks: first, he believes that Iraq is involved in relatively little international terrorism, and is most probably not implicated in the 9/11 attacks; second, he believes it unlikely that Iraq will use weapons of mass destruction directly or indirectly (i.e. through al Qaeda) against the U.S. except in a situation of total war. This actually speaks well of Pollack; he is not alarmist, and makes a sober, well-considered case.

Oddly, Pollack's book hasn't seen much widespread debate despite the fact that it got on the NY Times best-seller list, and has been plugged by a number of relatively widely-read commentators. However, this may be explained by both the fact that most people have, by this point, made up their minds on Iraq for good, and that many arguments on both sides ("No blood for oil!" or "Iraq=terrorists!") are pretty simplistic, whereas Pollack's book presents a complicated argument that runs counter to much established wisdom.

There's certainly plenty of room for disagreement on Iraq, and on much of what Pollack advocates. But he really is making the best case out there, and should be the baseline for principled pro-invasion arguments.