WASHINGTON, District of Columbia - The US secretaries of state and defence go before a Senate panel Tuesday seeking support to attack Syria over its alleged use of chemical weapons, warning failure to do so might embolden Hezbollah and Iran.
In what will be one of the most high-profile political set pieces in Washington in weeks, John Kerry and Chuck Hagel will testify to the Senate Foreign Relations committee.
America's top military officer, General Martin Dempsey, chairman of the Joint Chiefs of Staff, will also go before the panel.
Kerry will argue that failing to act in Syria "unravels the deterrent impact of the international norm against chemical weapons use," a senior State Department official said on condition of anonymity.
Inaction also "endangers our friends and our partners along Syria's borders... and risks emboldening Assad and his key allies - Hezbollah and Iran," the official warned.
As the White House battles for congressional authorisation to bomb Syria, two top Republicans warned Monday that a "no" vote after President Barack Obama had threatened action would be catastrophic.
Hawkish senators John McCain and Lindsey Graham emerged from an hour of talks with Obama suggesting that the White House could be mulling a wider military campaign in Syria than first thought, along with more robust support for the opposition.
Obama shocked Washington and the world on Saturday when he decided to seek support for military action in Syria from Congress, when it seemed US cruise missile strikes on President Bashar al-Assad's forces and assets were imminent.