Question: Who was a candidate for the Libertarian Party's 2012 nomination for President of the United States, that unsuccessfully challenged during his tenure, the fourth-ranking Republican leader in the House?
Sentence (from "Gary Johnson presidential campaign, 2012"): On May 5, 2012, after promoting his libertarian-oriented political positions to delegates, Johnson received the most votes at the convention and became the official 2012 Libertarian presidential nominee.
Relevant evidence: No