In an appearance Wednesday on Fox News Channel, Rumsfeld said he found Secretary of State John Kerry's Capitol Hill presentation of the case against Syria "persuasive and forceful," but he said he was concerned Obama might not be forceful enough in punishing Syria for the use of chemical weapons in an Aug. 21 attack in which more than 1,400 people were killed.
"My concern is, it seems to me, if you're going to do something you ought to do something that has a value and has a purpose, rather than sending signals out that what we're going to do won't be much, it won't last long and it won't end up with any changed circumstance on the ground," Rumsfeld said.
"The fact that the American people are confused and the fact that the Congress seems uncertain and the international community is not supportive is a reflection of the fact that the so-called commander in chief has not been acting as a commander in chief," he said. "He's not provided leadership."
Rumsfeld, a major architect of the U.S.-led invasion of Iraq in 2003, said if Obama isn't "going to do something that's worth doing it seems to me he shouldn't act."
He said the president did not need to ask Congress for its approval for a strike against Syria.
"Under the Constitution and practice we've seen that, we haven't had a declaration of war, for example, since World War II," Rumsfeld said. "Presidents, as commander in chief, have authority but they have to behave like a commander in chief it seems to me."