The New York Times reports: Secretary of State Hillary Rodham Clinton on Monday warned President Bashar al-Assad of Syria not to use chemical weapons and said that the United States was prepared to act if he ignored the warning.

“This is a red line for the United States,” Mrs. Clinton said. “I am not going to telegraph in any specifics what we would do in the event of credible evidence that the Assad regime has resorted to using chemical weapons against their own people. But suffice it to say we are certainly planning to take action if that eventuality were to occur.”

There have been signs in recent days of heightened activity at some of Syria’s chemical weapons sites, according to American and Israeli officials familiar with intelligence reports. Mrs. Clinton did not confirm the intelligence reports or say what sort of activity was occurring.

The Syrian Foreign Ministry, in a swift response, said the government “would not use chemical weapons, if it had them, against its own people under any circumstances.” The statement was reported on Syrian state television and on the Lebanese channel LBC.

Ostensibly, this reiteration of a red line President Obama already laid down in August has been precipitated by observations which suggest “some potential chemical weapon preparation.” Still, these tokens of assertiveness from the U.S. and its allies do nothing to abate the ongoing carnage. Indeed, they underline the fact that 40,000 Syrians killed without the use of chemical weapons is in some sense tolerable.

To be ripped apart by explosives or shrapnel, or crushed under the rubble of collapsing buildings — these are the methods of killing that fall short of Washington’s red line. And this begs the question: do warning’s such as Clinton’s actually constrain Assad’s behavior or merely confirm how much latitude he already has?