The results of this recent poll conducted by the Des Moines Register surveying 400 likely Iowa Republican caucus-goers was brought up in last night's GOP debate.

As you can see, support for civil unions is the biggest deal-breaker of any single issue (click here for full-size version):

Two more interesting facts from the poll: respondents say their two top picks are Mitt Romney (23%) and Michele Bachmann (22%) -- both candidates have signed the NOM Marriage Pledge -- and 21% of respondents say this year will be their first time participating in the Iowa caucus.