The tactic is to hold up an example that people can't disagree with as being 'bad', and claim you need new powers to fight this scourge. Illegal immigration is bad, so we need to be able to stop and search anyone at anytime in case they are undocumented. Drugs are bad, so we need to be able to tap phones and search houses without warrants, and set up checkpoints to screen anyone driving within 20 minutes of the Mexican border. And, child porn is bad, so we need to monitor all internet communications constantly to screen for it.
In each case, it's simply an excuse to grant unheard of powers to authorities, which they will then be sure to use for various other purposes which they didn't see fit to mention at the time. The actual solution to any of the problems used as the wedges don't resemble the proposed solutions, either.