Seems like everyone gets short-sighted when it comes to public policy, not just politicians. Businessmen too, when they involve themselves with politics, seem to forget anything beyond their noses when considering to weigh in on policy. I'm reminded of a speech given by economist Milton Friedman at the National Association of Manufacturers in 1978 (paraphrasing):
A businessman, in the course of running his business, will make long-range plans; he will think 10, 20 years down the road. He will not conduct his business based only on what is going to happen in 6 months. But when it comes to public policy, well...6 months is a long time to think ahead.
It seems like so few people think in terms of "this is being intended for X now, but what can be done with this kind of law in the future, and what precedents are set by its passing?" That's usually one of the first things in my mind when dangerous changes like the Patriot Act and the vote threshold change are implemented without an eye to the future.
It's incredible how short-sighted politicians can be. On side expands their power and act surprised when their successors use and abuse it.
A lot of the current wiretapping kerfluffle stems from the Republican's PATRIOT Act, IIRC.