U.S. grapples with Iraq invasion 20 years later

STORY: It was a war that began on shaky ground, in the aftermath of an America rattled by the 9/11 attacks.

DONALD RUMSFELD (JUNE 6, 2002): "The message is that there are known knowns. There are things we know, that we know. There are known unknowns. That is to say there are things that we now know we don't know. But there are also unknown unknowns.”

And 20 years after invading Iraq, the U.S. is still dealing with its consequences and a debate over who is to blame for the fallout.

From an empowered Iran and eroded U.S. influence in the Middle East, to ongoing combat with Islamic State fighters in Iraq and Syria, experts say the cost of U.S. involvement in Iraq since 2003 is vast and, in the end, enabled ethnic strife and complicated U.S. policy in the region.

It was early 2003, when then-U.S. President George W. Bush made the decision to oust Iraqi President Saddam Hussein by force -- a move supported by Bush's Undersecretary of State John Bolton, in the belief that Iraq was harboring weapons of mass destruction.

BOLTON (JANUARY 24, 2003): "We have very convincing evidence that Iraq maintains an extensive program for the production and weaponization of weapons of mass destruction and long range ballistic missiles that have been forbidden to it since the time of the Gulf War ceasefire resolution 687 in 1991.

No such weapons were ever found and soon after the invasion and the toppling of Saddam, the country exploded into violent chaos.

But looking back, Bolton tells Reuters that, despite Washington's mistakes, he believed removing Saddam justified the costs.

"It was worth it because the decision was not simply: 'Does Saddam pose a WMD threat in 2003? Another question was: 'Would he pose a WMD threat five years later?' To which I think the answer clearly was 'yes.'"

In Bolton’s telling, it was a decision made years later that was most consequential: the 2011 withdrawal of U.S. troops by then-President Barrack Obama.

"And then for Obama to pull out, pulled the rug out from underneath them yet again."

After years of unrest, the withdrawal left a vacuum soon filled by ISIS militants - seizing roughly a third of Iraq and Syria - and fanned fears among Gulf Arab states that they could not rely on the United States.

Jim Steinberg was a deputy secretary of state under Obama. He says the administration had little choice but to pull out given Iraqi resistance to keeping U.S. troops.

"There wasn't a really meaningful option for us to stay, unless we were to stay without the support of the government.

Steinberg said the war itself -- not the 2011 withdrawal -- raised deep questions about Washington's reliability as a partner.

STEINBERG: "We have this reputation of breaking but not repairing. And that's very dangerous because when you're in the region and you have to live with this problem, when we come in episodically and try to make things the way we want them to be, but then at the end of the day pull away.. the question is whether people aren't worse off for both parts - the intervention and then the pulling away - than if we had never intervened at all."

Bolton's belief that the intervention and removal of Saddam was worth the eventual cost is not held by many current and former officials… even in the Republican party.

According to the "Costs of War" project at Brown University, the U.S. price tag to date for the wars in Iraq and Syria is nearly $2 trillion, with more than 500,000 people killed as a direct result of the wars - including military, Iraqi and Syrian civilians, police, opposition fighters and media.

Obama in 2014 sent troops back to Iraq, where about 2,500 remain, and in 2015 he deployed to Syria, where about 900 troops are on the ground.

Today, U.S. forces in both countries still combat Islamic State militants, who are also active from North Africa to Afghanistan...

GEORGE W. BUSH (JUNE 8, 2002): "We can win the war on terror."

...years of conflict unforeseen in the early fervor to overthrow an Iraqi leader.