From the WaPo editorial 'The Spanish Response':

SPANISH VOTERS no doubt wished to rebuke the ruling Popular Party for its wrong-footed reaction to last week's terrorist bombing in Madrid, and its support for the United States in Iraq. Fair enough -- but it's hard not to be concerned about how the message was likely received outside the country, by the leaders of al Qaeda and other Islamic terrorist organizations. Before the bombing, the Popular Party was favored to win comfortably; after the devastating attack, and an al Qaeda statement saying its intent was to punish Spain for its role in Iraq, the election was swept by the opposition -- and its leader immediately pledged to withdraw Spanish troops and cool relations with Washington. The rash response by Jose Luis Rodriguez Zapatero, Spain's prime minister-elect, will probably convince the extremists that their attempt to sway Spanish policy with mass murder succeeded brilliantly...

An editorial in The Scotsman says this among others:

For the first time in modern history, a democracy has put up its hands in front of terrorists and said: "We surrender." Can any thinking person - including the Spanish, when they come to their senses - imagine that having tasted such success, al-Qaeda will abandon its murderous tactics?

It's good to be able to further discredit the left in general or at least the anti-war left. However, it would be better to prevent giving AQ a victory.

One way to prevent that would be for Zapatero to come out strongly against terrorism. Another would be to spin the election as a result of the electorate being supposedly lied to and not as a reaction to the attacks themselves.

The first probably won't happen, and the second is probably false and too nuanced.

UPDATE: In their editorial 'A Vote for Terror,' the NY Post says, among others, "The plain fact is that the Spanish electorate displayed craven cowardice by electing the Socialists..."

UPDATE 2: From the AP report 'After Spain, questions about Nov. election':

...analysts believe the ballot box rebuke of one of President Bush's closest allies in the war in Iraq could embolden terrorists to try the same tactics in the United States to create fear and chaos.

"That's an amazing impact of a terrorist event, to change the party in power," said Jerrold Post, a former CIA profiler who directs the political psychology program at George Washington University.

"The implications of this are fairly staggering," agreed political psychologist Stanley Renshon of City University of New York. "This is the first time that a terrorist act has influenced a democratic election. This is a gigantic, loud wakeup call. There's no one they'd like to have out of office more than George W. Bush."

And, from "Poland, Italy next 'terror' targets?":

"[Germany is] not the number one target at the moment, but because of the German armed forces deployment in Afghanistan and in the Horn of Africa, we are certainly in the Islamists' sights...

I expect that the terrorists will work their way through the U.S. allies. Poland and Italy, which are in Iraq as U.S. allies, are among those in danger."

UPDATE 3: From 'The Fall of Spain?' in Front Page Magazine:

And then the bombings took place — and many Spaniards decided that capitulation is the best part of valor, that mindless fear and manipulation are more powerful than common sense, civic values and pride. Despite public disclaimers by the PSOE leader and next Prime Minister, Jose Luis Rodriguez Zapatero, a national period of mourning and a declared suspension of the electoral campaign, PSOE operatives in Estremadura and elsewhere were inciting masses of party militants and clueless students to demonstrate against the government. The slogans used tell it all, in full stupidity and mendacity: "We want the truth before voting," "Our dead, your war," and "The people does not believe the lies of the PP." It all sounded as Dennis Kucinich was suddenly cloned.