Unlikely Republican front-runner Herman Cain faces close scrutiny on Tuesday when the party's hopefuls for president in 2012 debate in a gambling city famed for separating winners from losers.

Cain will be in the spotlight when candidates face off in a CNN-sponsored debate in Las Vegas at 8 p.m. eastern time, but his is not the only significant storyline.

Former Massachusetts Governor Mitt Romney has to sell himself to conservative voters who have been looking for an alternative.

Many political experts believe Romney will ultimately be the Republican nominee to face Democratic President Barack Obama next year, but he has a long way to go yet.

Texas Governor Rick Perry, a staunch conservative, has to prove he can hold his own on stage with his main rivals after four shaky debate performances that knocked him out of the front-runner position.

Cain, a former Godfather's Pizza chief executive and motivational speaker, has shot to the top of polls of Republican voters based on the simplicity of his 9-9-9 proposal to overhaul the U.S. tax code.

Experts have questioned whether his idea to cut personal income and corporate taxes to 9 percent, while creating a 9-percent national sales tax, would in fact raise taxes on lower- and middle-income Americans, hurting the most needy.

Although he is seen as a much-needed fresh face in politics with an inspirational style, Cain could run into problems as his economic plan, absence of foreign policy credentials and lack of governing experience, get more attention.

The '9-9-9' plan may communicate well, but as people take a closer look, they'll realize that more work needs to be done, Romney told the Las Vegas Review-Journal in an interview published on Tuesday.

A longshot candidate, former Pennsylvania Senator Rick Santorum, hinted on Monday he may raise some questions about Cain's 9-9-9 plan.

It's not as clean as he would like to make it out to be, Santorum told Radio Iowa. I give him credit for bringing some innovative ideas, but just because it's innovative and bold doesn't mean it's good.


Jennifer Duffy, an expert at the non-partisan Cook Political Report, said Cain is the latest to benefit from conservatives looking for someone other than Romney because they have doubts about the depth of his conservative beliefs.

Part of Cain's appeal is that he is not part of the process, he's not a politician, said Duffy. He's a very plain-speaking guy ... He's the only one out there now who actually has a 'new' idea.

Conservatives had first been captivated by Minnesota Congresswoman Michele Bachmann and then Perry before flocking to the Cain camp, an example of the wide-open nature of the race to find a Republican nominee with less than three months to go until voting in primary elections starts.

Romney has had steady debate performances throughout and retains solid support in polls. Republican strategist Scott Reed said he needs to show he is a good strong conservative.

Romney told the Las Vegas Review-Journal that Republicans will be persuaded to take his side based on his experience and a 59-point plan to turn the economy around.

I hope that as people take a closer look at my record and my vision, they'll say, 'That's the guy for us,'? Romney told the newspaper.

Perry has the task of recapturing the excitement when he first announced his candidacy two months ago. His debates, plus a position favoring college tuition assistance for illegal immigrants, has hurt him among conservatives.

Perry told the Las Vegas Review-Journal that voters would swing his way when they take a look at who it is on that stage that is conservative, that's always been conservative and that has a record of job creation.