For anyone solicitous of our precious civil liberties, the signing statement that accompanied President Obama's approval of the National Defense Authorization bill last month offers cold comfort.

Concerning the most controversial feature of the bill, the president wrote: "My administration will not authorize the indefinite military detention without trial of American citizens."

Should we trust him? This past September, Mr. Obama summarily executed U.S. citizen Anwar al-Awlaki in Yemen. Had Mr. Awlaki been residing in the U.S., does anyone doubt that Mr. Obama would have been willing to apprehend and detain him indefinitely?

I suspect that when Mr. Obama tells us that "American citizens" are exempt from indefinite military detention, he is thinking "John Smith," not "Osama bin Mohammed."

Mr. Obama may be hoping that his signing statement will reassure us — or at least the John Smiths among us — that we won't someday rue codifying these terrifying governmental powers.

Even so, does he think he will be the first and only president to interpret and execute this law? Of what use will this signing statement be when a future president chooses to disavow it?

Daniel Fleisher, Baltimore