The phrase "The economy, stupid" was coined by James Carville. He worked as a campaign strategist for Bill Clinton's successful 1992 presidential campaign against sitting president George H. W. Bush. Carville's original phrase was meant for the internal audience of Clinton's campaign workers.

But, working to dispel the perception that Mr. Bush was gaining on Mr. Clinton in their presidential race, the Democratic Party campaign tried to renew its focus on a message that was very important to all Americans. Some democratic political experts pointed to the U.S. economy, and they used the phrase "It's the Economy, Stupid" as a focal point to rally and obtain support. This was a slight variation of the phrase "The economy, stupid." Their slogan became a de facto slogan for the Bill Clinton election campaign.

More Info: en.wikipedia.org