Answer:
1. A debate is a discussion or argument between 2 or more people about a certain or giving topic/subject.
2. A presidential debate. Which is a public debate held during a general election campaign, where the candidates expose their political opinions and public policy proposals, and criticism of them, to potential voters. They are normally broadcast live on radio, television and Internet.
3. You are trying to debate on something. Example: "I'm debating weather to let you go to that party or not." or "I'm debating whether I should get this pizza or not"