I just finished reading Slate.com's summary of the major newspapers today. The NYT, the Wash Post, and USA Today all state that the biggest reason that Spain's Popular Party lost is how they handled the event - blaming ETA before there was enough evidence.
Now, personally, I suspect that this sort of thing would happen in lots of countries...if the US were in someone else's fight (say Vietnam) and days before an election the VietCong had somehow killed 200 US cits in a terrorist attack, McGovern might have won in '72.
But blaming Bush for the fall of this government is downright ignorant. Aznar chose to step in, knowing what his citizens thought of the whole deal. The new guy is saying he'll stay if there's a UN presence...
And again, personally, I'm not certain this was al-Qaeda. They haven't taken responsibility for anything before, not directly, and not two days after... ETA might have found an ingenious way to get rid of the Popular Party.