The question of U.S. involvement in Syria's two-year civil war has taken a new turn with the Obama administration saying the Syrian government has likely used chemical weapons against its people.
President Barack Obama last year, in attempting to encourage President Bashar Assad to show military restraint and to hold talks with his opponents, let himself get trapped into saying that use of chemical weapons would be a game-changer. That position was quickly transformed by those who favor U.S. intervention on behalf of the rebels into a "red line," which, if crossed, could lead to the United States joining the war.
France, Israel and the United Kingdom say they have evidence that the Syrian government has used chemical weapons in violation of the Chemical Weapons Convention, which outlaws their production, stockpiling and use and which was adopted by Syria, the United States and 186 other nations.
The White House sent a letter to congressional leaders Thursday saying U.S. intelligence agencies "assess with varying degrees of confidence that the Syrian regime has used chemical weapons on a small scale in Syria."
A more careful assessment is necessary, however, given the eight-year war in Iraq that was launched on false premises, including intelligence that the Saddam Hussein regime had biological, chemical and perhaps even nuclear weapons.
Another reason to check the claims more carefully is the general difficulty of gaining reliable intelligence from the confused situation in Syria. There are claims by the Syrian government and claims from rebels of many different colorations, including al-Qaida. A United Nations inspection team has been charged with investigating the chemical weapons allegation, but the Syrian government has not yet granted it permission to enter the country.
Mr. Obama would be wise not to act until the charges of chemical weapons use have been settled. U.S. involvement in the war should not be undertaken on the basis of shaky, unverified intelligence. Previously drawn "red lines" are, in general, a poor basis on which to conduct policy, particularly if it involves U.S. intervention in Syria.