WASHINGTON — The White House asserted Sunday that a “common-sense test” rather than “irrefutable, beyond-a-reasonable-doubt evidence” makes the Syrian government responsible for a chemical weapons attack that President Barack Obama says demands a U.S. military response.

As part of a major push to win the backing of a divided Congress and skeptical American public, Obama’s top aide made the rounds of the Sunday talk shows to press the case for “targeted, limited consequential action to deter and degrade” the capabilities of Syrian President Bashar Assad “to carry out these terrible attacks again.”

At the same time, chief of staff Denis McDonough acknowledged the risks that military action could drag the U.S. into the middle of a brutal civil war and endanger allies such as Israel with a retaliatory attack.

The U.S. is “planning for every contingency in that regard and we’ll be ready for that,” he told CNN’s “State of the Union.”

The U.S., citing intelligence reports, says sarin gas was used in the Aug. 21 attack outside Damascus, and that 1,429 people died, including 426 children. The Britain-based Syrian Observatory for Human Rights, which collects information from a network of anti-regime activists, says it has so far only been able to confirm 502 dead.

The Syrian government denies responsibility, contending rebels were to blame.

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