Four US presidential candidates are set to debate election issues in Chicago, a day after Barack Obama and Mitt Romney, the two main contenders, discussed their polices on foreign affairs in Florida. 

Tuesday's event, sponsored by the Free and Equal Elections Foundation, will feature Virgil Goode (Constitution Party), Rocky Anderson (Justice Party), Gary Johnson (Libertarian Party) and Jill Stein (Green Party).

Despite the fact that dozens of third-party candidates are running for president nationwide, most US voters have only heard Obama and Romney.

The country essentially has a two-party system and the big parties tend to get the top two slots on the ballot.

Their candidates get on the polls nationally without having to gather signatures, they are eligible for public funding and they are automatically entered in the national debates. None of that is true for third-party contenders.

Al Jazeera's John Hendren reports from Chicago.