Between 2009 and 2015, President Bush gave at least 200 private speeches that he was paid between $100,000 and $175,000 for (via Politico). Each speech lasts around an hour, which means he's been able to pull in millions of dollars on a part-time basis. Not too bad!

Former presidents profiting after their time in office has been decried by some political experts. According to Politico, University of Houston professor Brandon Rottinghaus has referred to the practice as "the post-presidential industrial complex at work." Still, former presidents who give lectures, and make plenty of money while doing so, robustly defend what they're doing.

Former President Bill Clinton told NBC News, "I gotta pay our bills. And I also give a lot of it to the foundation every year." The foundation he's referring to is the Clinton Foundation, which he founded in 2007.

The Wall Street Journal also reports that Bill and his wife, former Secretary of State Hillary Clinton, earned nearly $30 million from speeches in the years 2014 and 2015 alone.