Well it looks like the Madrid bombings were effective in ousting the old government. That's startling if you ask me. Governments like to position acts of terror as mindless and irrational but this shows that they can be an effective political tool. A radical minority effectively ousted a government. The future formula could be to use multiple terror attacks on vunerable targets a week before an election in a country.
How does the population react? It depends on a lot of things of course. If it happened that way in the United States, I suspect Bush would win hands down. If it happened in the UK, Blair would be out. I'm going to be edgy in the run up to the British elections and I'll avoid London commutes that's for sure.