It's great to read all you can about leaders and leadership, because you need multiple perspectives. That said, can you learn by watching politicians?
The answer may surprise you. You can indeed learn incredible amounts from watching politicians, but for the most part, if you observe them, particularly within the political process you can see, you will learn WHAT NOT TO DO, and WHAT NOT TO SAY.
Scary? it's not that our politicians are all terrible leaders, although many are. The problem is that what we get to see from the outside is politicians behaving from within a partisan political process that is ultimately competitive, and oriented towards getting one's way, or promoting a particular ideological agenda.
While the agendas of politicians DO include doing well for the country and the people they represent, that goal is subservient to the goal of election, or re-election.
As a result politicians often speak and act badly and come across as dishonest, overly slick, manipulative and hostile, particularly when they descend into negative election campaigns.
As someone interested in developing your own leadership skills, you can learn from watching and listening to them. During election campaigns, put aside some time to see how politicians are trying to "WIN". Put aside your own ideological beliefs about one politician or party, and listen carefully to your own gut reactions.
Are there things that politicians say in a quest to be elected that hit you in the pit of your stomach? What things "resonate" with you, in your gut?
Pay attention to different politicians and identify the things they do in similar ways. Many of those reflect a "win at all costs" perspective that is dangerous to effective leadership.