Heinz Doofenshmirtz suffered through a comically exaggerated neglectful, even abusive, claimed terrible childhood that left him scarred for the rest of his life. His parents were mentally abusive and ignored him, briefly disowned him, forced him to wear dresses or act as a lawn gnome, and frequently restricted him from doing even the smallest things. He also had to deal with many bullies, had no real friends, except for a balloon with a face painted on it, had issues with his body (a high squeaky voice and inability to grow facial hair), and generally failed embarrassingly at nearly everything he attempted. (The exceptions being cup stacking and, for a short time, shadow puppetry). His record in romance was equally dismal and almost always ended up with him being broken-hearted. Because of this, he built a robot to destroy love, which landed in the hands of Phineas and Ferb. Somehow he managed to woo and win the hand of Charlene and had one daughter with her before it fell apart and they divorced. Due to the cumulative weight of all these hardships he turned to evil and constantly attempts to seek vaguely directed vengeance with odd items he purchased off the Internet.
Doctor Doofensmirtz would make an excellent ruler of the Tri-State area due to his incredible intelligence and creativity. He made his way from the dregs of Drusselstein to creating Doofenshmirtz Evil Incorporated all on his own. In addition, the doctor's Inators are capable of shaping reality to his whim, allowing for anything to be possible under his leadership. Homelessness, poverty, food shortages, all a thing of the past with the right Inator!
Doctor Doofensmirtz's campaign platform is based on revenge against his brother, Roger Doofenshmirtz, for the years of preferential treatment his brother was handed. His long term goal also includes taking over the world, which I believe would be a good idea due to the above benefits.