I don't think Obama is viewed as being tough on international issues. Assad figured he could get away with whatever he wanted, and so far he's been right. It's been months since Assad first used chemical weapons. We should have taken a much harder stance on it then, but we didn't. So Assad just kept ramping up and now Obama is being forced to act, but now we have no initiative. Which is bad for military actions.
I do believe that if America has the power to stop atrocities and we choose to stay out of it, it's immoral. If we see a murderer and we can stop him but we don't, won't we all end up with Peter Parker angst? No one wants that noise.
I know everyone wants to believe that people are inherently reasonable and if they just had enough food, water, roofs over their heads, and a flatscreen TV, they will be content and just leave everyone else alone, but its just not the case. Or rather, we don't know if it's the case or not because people hoard the flatscreens instead of sharing. Because people are greedy.
So now we've got this situation in Syria, and we really don't know what will screw the world more- Assad winning or rebels winning. What is clear to me, we (and I mean the reasonable people of the world at large) should not allow the use of chemical or biological weapons. We just don't want wars to go down that route. They will inevitably be used, but we can hold off that horror at least a little while by responding strongly against those that use them. So far the President has been back pedaling and weak in his response. Hopefully, he can also be strong.