From this:

LONDON (Reuters) - Islamic militants will see the defeat of Spain's Popular Party and the country's planned withdrawal from Iraq as a victory for their cause, encouraging more attacks aimed at political ends, security experts say...

"Clearly, they thought very hard about the way in which they might achieve a massive political impact in Spain," said Paul Wilkinson, chairman of the Centre for the Study of Terrorism and Political Violence at Scotland's St Andrew's University.

"I think what it shows is that the very sophisticated and ruthless terrorists of the 'new terrorism' variety -- al Qaeda -- do think carefully about having a maximum strategic impact."

[David Claridge, managing director of Janusian Security Risk Management] said: "Amongst the Islamist community there clearly was discussion and thought around Spain as a potential target and Spain being vulnerable to terrorism as a means of causing political change."