President Barack Obama, acutely aware of the cost of war, rarely seeks to wage it, so the sharpening of US rhetoric on Syria may be fateful and significant.
For months, the Nobel peace laureate resisted being sucked into the sectarian quagmire in Syria, despite the carnage unleashed on civilians in a war in which around 100,000 people are said to have have died.
He resisted calls for no-fly zones and demands from within his own war council to arm the rebels fighting President Bashar al-Assad, fearing weapons could end up with jihadists.
But America's gray lines on Syria darkened on Sunday with a blunt statement by a senior White House official that there was "very little doubt" that Assad's forces had turned chemical arms on civilians last week.
Syria's offer of access to the attack site was spurned as too little, too late.
A senior official traveling with Defense Secretary Chuck Hagel bolstered the line Monday, noting "strong signs" chemical agents were used.
The rhetoric was notable because it appeared to offer Obama little wiggle room after he warned a year ago that the use of chemical weapons would cross a US "red line" and came as military assets moved into place off Syria.
There is now a strong sense in Washington that the use of force against Syria, which however limited would embroil the United States deeper in the vicious civil war, is inevitable.
"I think a response is imminent," said Republican Senator Bob Corker, a well informed voice on foreign policy.
"I think you are going to see a surgical, proportional strike against the Assad regime for what they have done and I support that," Corker said on MSNBC.
The shift in mood is all the more remarkable because only three days ago, Obama was warning of the danger of new Middle East adventures.
He did describe the chemical attack outside Damascus, which the opposition says killed 1,300 people, as a "big event" hinting at a strong US response.
But Obama, who has pulled US troops home from Iraq and is doing the same in Afghanistan, expressed extreme skepticism about a new Middle East entanglement.
Signup to our newsletter and follow us on Facebook and Twitter!
He warned in an interview broadcast by CNN Friday of "very expensive, difficult, costly interventions" that breed resentment in the region and chided those who jump into "stuff that does not turn out well, gets us mired in very difficult situations."
It was not the first time Obama expressed caution about wielding US power in the Middle East, a fact conservative critics have used to brand him as "weak" and guilty of presiding over diminishing US global influence.
In May, he said he could only act on the best possible evidence of chemical weapons use in Syria, making sure he was "making decisions not based on hope and a prayer, but on hard headed analysis in terms of what will actually make us safer and stabilize the region."
Obama's defenders point out he is hardly a reluctant warrior -- he leads a ruthless and shadowy drone war against terror suspects worldwide and took a huge risk with the raid to kill Osama bin Laden.
But Obama made his name as a political candidate raging against "dumb wars" and said when accepting the Nobel peace prize that war "is never glorious and we must never trumpet it as such."
In the same speech Obama quoted Martin Luther King, saying violence never brings permanent peace but merely creates "new and complicated" problems, sn insight into his preoccupation at the unforeseeable consequences of military action.
In many ways, Obama's entire presidency has been a reaction to what he sees as the unwise over-projection of power in the Bush administration, which led America into the sectarian crossfire in Iraq.
He also often argues that the United States can no longer go it alone in foreign wars, and must act in accordance to international law.
So any US action in Syria will only take place with a coalition of foreign allies.
What prompted the rhetorical shift from the White House is unclear.
It could be that unequivocal US intelligence suggested complicity in chemical warfare by Assad's regime, which would put Obama's personal credibility on the line following his "red line" comments.
Washington may also be keen to demonstrate that the long taboo on the use of chemical weapons must be maintained.
Administration officials reject the idea that the president vacillates on the use of force, or is guilty of "leading from behind" in operations including the NATO air assault on Libya.
They say prudence does not equal weakness.
"Several instances in my presidency, when I said I was going to do something ... I ended up getting it done," Obama said in May, citing the raid that killed Osama bin Laden and the NATO operation that toppled Libya's Moamer Kadhafi.