According to the Maryland elections site, there are 18 active Democratic candidates for the Senate seat. Should the League of Women Voters have had a debate with all of them? What useful information would the voters get if 18 people were trying to debate at once (even assuming that none of them are nutbars)?
The League is an independent organization that is trying to provide a service to voters. Accordingly, they set a standard of who to let in based on who they thought, based on poll numbers, actually had a chance.
It is certainly easy to disagree with the standard they set and reasonable people could certainly think that 15% was unfair. But... their debate, their rules. :shrug:
http://www.elections.state.md.us/current_election/candidates/All_Offices.html#office_007Candidate: Benjamin L. Cardin
Party: Democratic
Status: Active
Candidate: David Dickerson
Party: Democratic
Status: Active
Candidate: George T. English
Party: Democratic
Status: Active
Candidate: James H. Hutchinson
Party: Democratic
Status: Active
Candidate: Anthony Jaworski
Party: Democratic
Status: Active
Candidate: A. Robert Kaufman
Party: Democratic
Status: Active
Candidate: Allan Lichtman
Party: Democratic
Status: Active
Candidate: Thomas McCaskill
Party: Democratic
Status: Active
Candidate: Kweisi Mfume
Party: Democratic
Status: Active
Candidate: Josh Rales
Party: Democratic
Status: Active
Candidate: Dennis F. Rasmussen
Party: Democratic
Status: Active
Candidate: Bob Robinson
Party: Democratic
Status: Active
Candidate: Theresa C. Scaldaferri
Party: Democratic
Status: Active
Candidate: Mike Schaefer
Party: Democratic
Status: Active
Candidate: Charles Ulysses Smith
Party: Democratic
Status: Active
Candidate: Blaine Taylor
Party: Democratic
Status: Active
Candidate: Joseph Werner
Party: Democratic
Status: Active
Candidate: Lih Young
Party: Democratic
Status: Active