The cartoon shows Barack Obama as the 'world's policeman' sitting at the wheel of his patrol car. However, he isn't going anywhere because his car's been clamped.
The cartoon is a metaphor for the effect of US public opinion on Obama's Syria policy. After the chemical weapon attack, Obama was keen to launch a military strike against the Syrian regime. He then decided to put the matter before Congress, and is now engaged in talks with Russia over the latter's plan to get Syria to give up its chemical weapons.
1. A wheel clamp, also known as wheel boot or Denver boot, is a device that is designed to prevent vehicles from being moved. In its most common form, it consists of a clamp that surrounds a vehicle wheel, designed to prevent removal of both itself and the wheel. In the United States, these devices became known as a "Denver boot" after the city of Denver. Colorado was the first in the country to employ them, mostly to force the payment of outstanding parking tickets. [Wikipedia]
2. Americans say that a car has been booted, whereas in Britain we use the word clamped.