Probably bought them with some of their campaign cash. There are many places online where they are for sale cheap.
http://www.ebay.com/sch/i.html?_nkw=buy%20twitter%20followers&clk_rvr_id=524583547183&adpos=1o1&MT_ID=69&crlp=10234234972_2416792&device=c&geo_id=10232&keyword=buy+twitter+followers&crdt=0
1¢ per twitter follower