At home and abroad, America's disastrous war in Iraq hangs over the debate on Syria, feeding skepticism that US military action can deliver as promised.
"It's the elephant in the room," said Larry Korb, a former Pentagon official and a senior fellow at the Center for American Progress.
"Had we not had the Iraq war, there would be no real question here," he said, suggesting that proposed strikes on Syria would have been "approved overwhelmingly" by Congress.
Now, however, President Barack Obama faces stiff resistance as he tries to persuade lawmakers and world leaders to punish the Syrian regime's alleged use of chemical weapons.
In a painful irony, Obama -- the Democratic senator who won the White House partly thanks to his opposition to the Iraq invasion -- now finds himself arguing for another "war of choice" in the Middle East without UN backing.
The strange twist has not been lost on Obama, who once castigated his predecessor for pursuing a war of "undetermined length, at undetermined cost, with undetermined consequences."
Acknowledging that "there's a certain suspicion of any military action post-Iraq," Obama has promised repeatedly that there will be no US boots on the ground in Syria.
And, in presenting its case for action, the Obama administration has been anxious to avoid accusations of hyping the intelligence, which tarnished the rationale for the Iraq invasion.
But for the most part, the argument against bombing the Syrian regime has not hinged on the credibility of intelligence reports.
Instead, skeptics have questioned the purported effect of the planned missile strikes and warned of unintended consequences.
Lawmakers in Washington and diplomats abroad have not forgotten being told by George W. Bush's deputies that toppling Saddam Hussein would be a "cakewalk" with a modest price tag.
Instead, US forces stayed in Iraq for eight years, with 4,400 troops and an untold number of Iraqi civilians killed, at a cost of about three trillion dollars.
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"I suspect a lot of the opposition to using force now stems from the bad taste that Iraq left in people's mouths," said Stephen Biddle, a professor of political science and international affairs at George Washington University.
"And it's made them skeptical of claims that you can use a little bit force and be done," he said.
According to a CNN poll released Monday, 59 percent of Americans said Congress should reject US military action against Syria and 69 percent said it is not in the country's national interest to get involved in the conflict.
Despite the opposition to strikes, the survey showed most Americans believe the administration's charges that President Bashar al-Assad's regime used chemical weapons.
The hangover from the Iraq conflict has fed deep skepticism among America's allies, and its impact was on full display when British MPs voted against taking part in any American-led missile strikes.
"The well of public opinion was well and truly poisoned by the Iraq episode and we need to understand the public skepticism," said Prime Minister David Cameron, whose call for intervention went down to resounding defeat in the British parliament.
There is little enthusiasm for intervention among US military leaders, who saw the Iraq debacle unfold and came away wary of nation building and "regime change."
Much of the top brass would prefer to avoid any action that could draw the United States into the cauldron of Syria's civil war.
The chairman of the Joint Chiefs of Staff, General Martin Dempsey, has endorsed "limited" strikes on Syria, but he has said Iraq weighs heavily on his mind and has repeatedly warned of the risks of trying to oust Assad.
"Once we take action, we should be prepared for what comes next. Deeper involvement is hard to avoid," he wrote last month in a letter to senators.
The crisis over Syria has led commentators to invoke references to the "ghost" of the Iraq war and the "burden" of Bush's legacy.
Bush "gave every world leader, every member of Congress a reason to keep the dogs of war on a leash," wrote Timothy Egan in The New York Times.
"The isolationists in the Republican Party are a direct result of the Bush foreign policy," he wrote.
"A war-weary public that can turn an eye from children being gassed - or express doubt that it happened - is another poisoned fruit of the Bush years."