Why don't they exercise more competence with the powers they currently have, before asking for more? (For example, investigate and arrest a some of the crooks whose suspect activities derailed the U.S. economy.)

I'm sorry if this comment seems off topic, but I feel it's in line with some overarching observations. Law enforcement is hardly currently powerless. Where they fail is not in legal powers, but in execution and focus. The latter particularly suffers, further, when career timeframe work is continually jerked around and undermined by partisan politics.