Department of Homeland Security
The Department of Homeland Security or DHS is a massive government structure that includes several other government structures composed of other government structures. Given how authoritarians love large centralized things it's arguably a surprise this didn't happen earlier.
No author would have named such a thing the Department of Homeland Security. Reality couldn't possibly be this messed up, right?
What Is This?
It is the most recent consolidation of multiple government agencies into yet another, even bigger bureaucracy. It includes a previous such consolidation, FEMA.
Why Does This Exist?
The events of 11 September 2001 were blamed on a lack of communication between already too-powerful government entities whose primary purposes weren't actually protecting the US. So naturally combining them and sticking some potentially uncorrupted organizations under the same umbrella must obviously make everything right in the world.
What Has It Done?
It's the meta case for several of its child agencies accomplishments: The Katrina response, Mandatory sexual molestation at airport police states, construction of FEMA camps, targeting US citizens as the real threat,
It also highly opaque and blows through an amazing amount of money, and is a magnet for fraud, waste, and abuse.
If national security is a concern of yours, they deal with this fairly effectively with badly protected databases of secret and top secret information, all the while making sure that the people who might put a stop to this situation don't find out about it. Rest assured that China, North Korea, Iran, et al have minimally fettered access to this information.
What's Wrong With It?
What ISN'T wrong with it might be an easier question to answer.
How Do We Get Rid Of It?
Abolishing it and all of its components might be hard to get through the legislature, although it does make for a highly satisfying paper exercise.
Most of these entities existed under other departments and could be moved there if the department itself is the easiest thing to eliminate.
The Coast Guard, assuming it is to continue as a government entity, might be better placed under the Department of Defense, as it's one of the few components of that that actually would be defensive in nature. ...As soon as we get rid of its non-defense functions.