Barack Obama was and is a failed president. His domestic policy achievement, Obamacare, caused Democrats to lost the most state and federal legislative seats since the 1920s. He after having his wings clipped by voters, his second term agenda had to turn to foreign policy, as his domestic agenda hit a Republican wall.
Obama doesn't believe in peace through strength, or protecting allies like Israel. He believes the opposite, that the United States and Israel were the sources of the world's problems, not solutions. As such, he wanted to bolster Iranian power, as he thought they would be better at managing the region than we were. He also wanted to pass the buck of an aggressive Iran on to someone else. For this and other reasons, the Iran Deal is a disaster; we can give you five more reasons why the last one being the scariest.