Why attack Syria?

I don't understand what is the rationale for the Syria attack -- they shot up a building under construction and blew some stuff up and killed a few people, then flew back to Qaim.
Was it just a bunch of rogue soldiers "taking matters into their own hands"?

A U.S. military official said the raid by special forces targeted the foreign fighter network that travels through Syria into Iraq. The Americans have been unable to shut the network down in the area because Syria was out of the military's reach.
"We are taking matters into our own hands," the official told The Associated Press on condition of anonymity because of the political sensitivity of cross-border raids.

But later in the article we find out that there aren't large numbers of foreign fighters coming into Iraq anymore:

The flow of foreign fighters into Iraq has been cut to an estimated 20 a month, a senior U.S. military intelligence official told the Associated Press in July.

That's like five people a week, not all of whom would be entering at Qaim anyway.
So was the American military just showing off? Or are they trying to provoke a war with Syria? And what would be the idea behind that -- do they think starting another needless war would actually help McCain win this election?