You can only get a Power of Attorney for your father if he agrees to give it to you. You would have him sign a form, preferably one drawn up by an attorney (so you are sure that it will do what it is supposed to do, if and when you need to use it). Given your father's history, it sounds unlikely that he is going to voluntarily agree to this.
If you truly believe he is a danger to himself and can no longer manage his affairs, then you may need to resort to guardianship/conservatorship proceedings. These are handled in the probate court in the county where your father lives.
You would need to file a petition with the court. The court will appoint a "guardian ad litem" to investigate the facts and make a recommendation to the judge. The GAL will try to determine if your father needs assistance and who would be best to provide that to him. If your father can express an opinion, his preference *may* be taken into account. If your father is determined not to have YOU act on his behalf, then the court *might* appoint a disinterested third party (often a county public administrator) to act as guardian and / or conservator. (The guardian is in charge of the physical custody of the ward and can make medical treatment decisions, as well as living arrangements. The conservator is in charge of the ward's financial resources. Often the same person performs both jobs.) A hearing is usually required. The estate would need to pay the costs of the proceedings, if it can afford to do so.
Best of luck to you as you deal with this difficult situation.