Months of his supporters going insane on social media with how incorrect polling was...despite no money...poor organization and a message that seemed to be summed up in "LEGALIZE POT!, disarm America and Trump is evil." Rand entered Iowa polling under 5% as he had been since the summer. He was insisting that polling was inaccurate..well...looks like the voters were accurate enough though. He is dropping out of the race.
It remains to be seen where the last Libertarians will head in this cycle.