"The Buck Stops here," said the famous sign on Harry S Truman's desk, encapsulating the lonely dilemmas power presents to US presidents, one of which now confronts Barack Obama over Syria.
Obama is trapped in a conundrum, partly of his own making, after Syria apparently called his bluff by using chemical weapons in an escalation of an vicious civil war -- and in the process, challenged a US "red line."
Unless he can find wiggle room, the president may have to reconcile the conflict between a need to prove his personal credibility with a desire to avoid being dragged into another Middle Eastern war.
Obama mused on the humbling demands on the modern president when he honored George W. Bush in Texas last week.
"There are moments where you make mistakes. There are times where you wish you could turn back the clock," he said.
Obama might have been reflecting on the moment last August when, in the heat of his re-election bid, he warned President Bashar al-Assad that using or moving chemical weapons would change his "calculus" on Syria.
That comment came back to haunt him last week, when news broke that US intelligence believes Syrian forces did use chemical weapons.
The size of the action, its human toll and whether it was designed as a deliberate test of Obama's limits or to draw America into a new quagmire were unclear.
But the revelation sparked heat on Obama to live up to his threats, creating a messy political problem, as calls mounted for him to arm anti-Assad rebels, pummel Syria with air power or establish a no-fly zone.
"The president did say that there's a red line, and once the United States lays out a red line, some action has to be taken," said Peter King, a congressman from New York on NBC's "Meet the Press."
Obama's predicament laid bare the risk in laying down "red lines" on key national security crises: sooner or later someone might cross them.
It is for this reason Obama, unlike Israeli Prime Minister Benjamin Netanyahu, is reluctant to pinpoint the moment when Washington might strike to thwart any Iranian breakout towards nuclear weapons.
Another problem with the Syria "red line," according to Republican Senator John McCain, is that it convinced Assad any atrocity short of using chemical weapons would not rouse Washington.
"The president drew a red line on chemical weapons, thereby giving a green light to (Assad) to do anything short of that, including Scud missiles and helicopter gun ships and air attack strikes and mass executions," he told NBC.
Obama's actions on Syria will be closely watched -- especially in Tehran.
"It's no longer a question of just Syria. It has a lot to do with his personal credibility," former Middle East peace negotiator Aaron David Miller told AFP.
"Everyone says no to the United States these days without cost or consequence. So how he comports himself with respect to Syria will be read, interpreted, by the Iranians and others with great significance."
His media team's linguistic contortions reveal the tricky ground Obama is on.
Asked Monday to define the red line, spokesman Jay Carney refused to say whether a small scale use of chemical weapons would cross it.
The White House, wary of the kind of faulty intelligence that prefaced the Iraq war, wants more clarity on the alleged chemical attacks.
US history is pockmarked by unwise decisions driven by a desire to spare the blushes of a president -- including the reluctance of Lyndon Johnson and Richard Nixon to look weak by retreating from Vietnam.
"It can't be that a president just makes the decision to use force -- to send American troops into a war to protect his credibility," said Julian Zelizer, a Princeton University professor of history.
"We want him to make this decision based on a true evaluation on what is going on in Syria and when force is absolutely essential."
While using chemical weapons against civilians in Syria would present Obama with a grave humanitarian decision, Washington is most concerned about what will happen to the weapons when Assad falls.
The fear that motivated the war in Iraq -- that terror groups could get hold of weapons of mass destruction -- could become reality and would likely guarantee US military action.
But Obama does not yet appear to be at that point.
There were signs Monday he may try to leverage the alleged use of chemical arms to convince Russia to finally get tough with its ally, when he raised concern about the situation in a call with President Vladimir Putin.