Are they reacting to terrorism? Or are they using terrorism as a pretext to expand their powers (or to achieve whatever goal they have)?

You're asking whether it's sincere or not? Not sure. But the political support from the public that they need to have power is, i think, sincere because the public is legitimately afraid of all this "risk" they're exposed to.

"Or are they using terrorism as a pretext to expand their powers"

That is exactly what is happening.