Rand was doing exceedingly well for quite a while after the Romney endorsement. He was leading national preference polls for the Republican presidential nomination for substantial portions of 2013 and 2014. His decline this year has stemmed from a set of converging factors:
-The PATRIOT Act/NSA filibuster, which turned a great number of establishment security-hawk Republicans against him for good
-The heightened state of public fear and hawkishness brought on by the Islamic State
-Certain actions (signing the Iran letter, opposing the Iran deal) which alienated significant numbers of his anti-establishment, anti-war followers
-The crowded field distinguished by the emergence of several candidates (Trump, Sanders, Cruz) whose crossover appeal sapped support from Rand