....and the independents are spoilers for which party?
Pressler was U.S. Senator (R) from South Dakota 1979-1997; this is his old seat, currently held by the crippled Tim Johnson (D).
The other one, Gordie Howie, doesn't have much out about himself:
Howie was elected to the South Dakota House of Representatives in the 2004 elections, serving in that body from 2005 to 2009. He was then elected to the South Dakota Senate in the 2008 elections, serving in that body from 2009 to 2011. In the spring of 2009, he founded and became president of Citizens for Liberty, a conservative group affiliated with the Tea Party movement.
Howie ran for Governor of South Dakota in the 2010 elections, with former State Senator Kermit Staggers as his running mate. Howie finished fourth out of five candidates in the Republican primary, with 10,430 votes (12.4%).
He is running for the United States Senate as an Independent in the 2014 elections. He has stated that he is running to ensure there is a "true conservative choice" because Republican nominee former Governor Mike Rounds is too moderate.
So, essentially, three (R)s, one (D), in this race.