– Ben Carson and Marco Rubio, trying to survive and thrive in the spotlight that surging presidential candidates must endure, face a huge new test at Tuesday's Republican debate. Donald Trump and Ted Cruz also are in for a crucial night. The stakes are high for national newcomers Carson, Rubio and Cruz, because the more people heard about them the more they liked, giving each enormous upside — as well as potential to disappoint and plunge.

The debate's focus is supposed to be the economy. That was also billed as the topic of the last one, which at times became a free-for-all. The furor over that debate's tone prompted campaign officials to seek changes, but no agreement could be made so the format's not changing. The two-hour debate at the Milwaukee Theatre will start at 8 p.m. CST. The undercard — with Chris Christie, Mike Huckabee, Rick Santorum and Bobby Jindal — begins at 6 p.m. CST. Here are four questions for the main debate:

Can Rubio take more hits?

The U.S. senator's surge to prominence last month began with his passionate defense of his Senate voting record. Former Gov. Jeb Bush kept tumbling after his wan challenge to Rubio. Since then, Rubio's faced questions about using a Republican Party credit card for personal expenses while in the Florida Legislature. Saturday, his campaign released an accounting of the expenses, and chances are Rubio will be armed with pointed responses to any critic. Can he stay cool when defending himself? And will the public buy his explanations?

Can Carson tackle key questions?

The retired neurosurgeon has been tackling questions about his personal background and views. He could be grilled Tuesday on his history with Mannatech, a nutritional supplements firm, as well as dealings with the U.S. Military Academy, assertions that Egypt's pyramids were built to store grain, and just how violent he may have been as a teenager.

Will Trump be bombastic or reasonable?

The real estate mogul toned down his rhetoric at the last debate. But in recent media and campaign appearances he's berated his rivals. Rubio, Trump said, is "a disaster with his credit cards." After a new national poll last week showed Carson ahead, Trump told Fox News, "Ben can't do the job." Trump has to be more statesmanlike, but there's a risk for Rubio and Carson, too. They need to show they have what it takes to stand up to world leaders, but first they have to show they can stand up to Trump.

Can anyone new break out of the pack?

Cruz is the best bet. McClatchy-Marist poll found the more a majority of Republicans see of the senator from Texas, the more they like him. For the rest, it's getting late, and many remain stuck below 5 percent. Earlier bids to be distinctive haven't worked. Former executive Carly Fiorina was the star of the September debate, but her momentum fizzled. John Kasich, the governor of Ohio, went on the attack at last month's debate but it didn't help.