I think a significant amount has been accomplished in Iraq, although I'm not sure how long-lasting or stable our accomplishments may be. In 25 years, our efforts in Iraq may be completely wiped out, leading historians to say it was all for naught.
First of all, we eliminated a leader who murdered his own people and thumbed his nose at the UN and the western world.
Furthermore, the invasion of Iraq was a brilliant strategic military move in the sense that it drew thousands, perhaps millions of insurgent anti-American warriors into that theatre.
The Bush administration calculated that, if we are to wage a war against anti-America/Israel terrorists, it was wise and prudent to wage that war in Iraq instead of somewhere else. This was the brilliance of the invasion.
In fighting the so-called "War on Terror" in that theatre, among other places, we not only kept American deaths at a bare minimum (and this is a largely over-looked historical accomplishment that I'll get into in the next paragraph) but we also accumulated great amounts of intelligence...intelligence which is and will help our efforts in other theatres like Afghanistan, Iran, Syria, etc.
During a training exercise in World War 2...a training exercise...America lost 12,000 military personnel. During six years of the war in Iraq, America has lost an astonishingly low number of 4,000 military personnel. This must rank as one of the great achievments in military history, yet it largely goes unnoticed or underreported by the mainstream media.
Remember, the ultimate agenda for this "war on terror," the plan set forth by the PNAC, was to wrest geo-political control in that region of the world. By "occupying" or heightening our presence there, the US can more readily control and influence, and monitor the complicated movements in that all-important region.
We have accomplished much. But we face a very likely chance that we may undo all the accomplishments unless we are vigilant. And this transcends politics. Both Republicans and Democrats realize the long-term implications. That is why most Democrats, including the Clintons and Joe Biden, actually voted in favor of the invasion of Iraq.