As opponents of Syrian President Bashar al-Assad braved the frontlines around Damascus to try to deliver tissue samples to UN inspectors from victims of Wednesday's poisoning, Mr Obama brushed over an interviewer's reminder that he once called the use of chemical weapons a "red line" for US action on Syria. He played down the chances of Assad cooperating with a UN team that might, if given access soon, provide conclusive evidence of what happened.
In any case, the President said he would not react in haste to calls for US intervention that would "mire" Americans in an undertaking counter to their long-term interests.
Noting budget constraints, problems of international law and the US casualty toll in Afghanistan, Mr Obama said: "Sometimes what we've seen is that folks will call for immediate action, jumping into stuff that does not turn out well, gets us mired in very difficult situations, can result in us being drawn into very expensive, difficult, costly interventions that actually breed more resentment in the region.
"The United States continues to be the one country that people expect can do more than just simply protect their borders. But that does not mean that we have to get involved with everything immediately.
"We have to think through strategically what's going to be in our long-term national interests."
Asked about his comment - a year to the day before poisonous fumes hit sleeping residents of rebel-held Damascus suburbs - that chemical weapons would be a red line for the US, he replied: "If the US goes in and attacks another country without a UN mandate and without clear evidence that can be presented, then there are questions in terms of whether international law supports it."
Russia and China have vetoed United Nations Security Council moves against Assad in the past and oppose military action.
International powers, including Moscow, have urged Assad to cooperate with a UN inspection team, which arrived on Sunday to pursue earlier allegations of chemical weapons attacks and to give them access to affected areas before evidence deteriorates.
However, there was no public response from the Syrian government, whose forces have been pounding the region for days, making any mission by the international experts perilous, as well as potentially destroying evidence. The Syria government denies being responsible and has in the past accused rebels of using gas.
UN Secretary General Ban Ki-moon, who is despatching a top official to lobby Assad, said: "I can think of no good reason why any party, either government or opposition forces, would decline this opportunity to get to the truth of the matter."
Russia, Assad's main arms supplier, said the opposition was preventing the investigation of what happened, while Britain said it now believed Assad's forces carried out the attack.
Syrian officials say allegations against their forces are "illogical and fabricated". They point to the timing of the attack, just days after the arrival of UN inspectors.