For what little it's worth, almost all the early US commentary on the Spanish elections seem about 98% mistaken to me. As far as I can tell, the moral of the story has nothing to do with strength or weakness, appeasement or terror, and relatively little to do with the costs of being GW Bush's (or the US's) friend and ally. It even has relatively little to do, alas, with the political costs of entering precipitously into wars of choice.
No, the moral of the story is this: voters don't like to be lied to, and in politics the coverup often costs more than the crime. The Spanish voters decided, apparently correctly, that their government had lied to them when it blamed ETA, local terrorists, for an act of barbarism committed by al Qaeda, foreign terrorists.
Which means that the 2% of recent commentary I agree with is the part that says this is bad for Bush: as the Bush lies like a rug meme gathers steam (the latest outrage about muzzling Richard S. Foster, Medicare's favorite actuary — only reinforces it), the idea that the US voters will punish Bush for lying, like the Spanish voters punished José María Aznar will begin to take hold.
Update: Seems like someone agrees.
Update (2): More agreement.