How?
As pointed out in the European press and Josh Marshall picked it up, the Spanish public voted against the conservatives not because they sent troops to Iraq in support of the US, but that the Spanish government misled and lied to the Spanish people about who conducted the attack. They kept ignoring evidence that it was Al Queda related and blamed it on ETA .
They lied to their own people for political purposes, they exploited their position and spoke to their own people in bad faith.
The Bush administration also misled their own people and exploited a terrorist event for their own political purposes. They misled the American people about who was involved in 9/11 and they used it to achieve their own political purposes, to attack Iraq.
That's the meme -- the Spaniards voted their government out for misleading them over a national tragedy and that is just what the Bush administration has done with Iraq and 9/11.