Republican presidential candidates are set to hold their latest debate at a Las Vegas casino Tuesday evening.

Some polls show former pizza company executive Herman Cain in the lead. The six other Republican contenders participating in the debate are expected to press him on his plans for an overhaul the US tax code.

Cain, who has never held office, but is popular among conservatives, has gained attention for his “9-9-9” plan which cuts personal and corporate income taxes to nine percent and creates a nine percent national sales tax.

Cain is the only African-American in the Republican field and has gained notice with a smooth speaking style and an ability to connect with voters.

Other topics expected on tonight's agenda include the economy, illegal immigration and border security.

In addition to Cain, others participating in Tuesday night's debate are former Massachusetts governor Mitt Romney, Texas governor Rick Perry, Minnesota Representative Michele Bachmann, Texas Representative Ron Paul, former Pennsylvania Senator Rick Santorum and former House Speaker Newt Gingrich.

Former Utah Governor Jon Huntsman will not participate in the debate in protest of Nevada's decision to move up the date of its caucus to January 14.

Meanwhile Tuesday, the Iowa Republican Party has set January 3, 2012 as the date for the first state contest to select a party presidential candidate.

The Iowa caucus is seen as the crucial first step in narrowing down the field of candidates.