Six things to watch for at the Las Vegas Democratic debate

Two hours on a live debate stage Tuesday should be ample time for the Democratic underdogs battling front-runner Hillary Clinton to make a beneficial impression on voters — or to acutely disappoint them, politics watchers say.

"The debates will alter the race," said Stephanie Cutter, a Democratic strategist and top staffer in the President Obama's 2012 re-election campaign. "Clinton will no longer be running against herself — the debates will force a choice, but only if she strongly stands by her positions, record and beliefs and doesn't get pushed to the left by others."

Nearly 23 million viewers tuned in for the last GOP debate, featuring the smash-mouth antics of Donald Trump and his rivals' attempts to weaken him. Will the Democrats be able to engage as many people for their first debate, set to begin at 9 p.m. ET (coverage starts at 8:30) on Tuesday in Las Vegas?

"Hillary should appear in character as 'Val,' " joked Tracy Sefl, a former senior adviser to Ready for Hillary, the super PAC that laid the groundwork for Clinton's campaign. Clinton portrayed a bartender named Val in a recent Saturday Night Live sketch.

Those competing Tuesday are Clinton, a former secretary of State; Vermont U.S. Sen. Bernie Sanders, her closest rival in the polls; former Maryland governor Martin O'Malley; former Virginia senator Jim Webb; and former Rhode Island governor Lincoln Chafee.

Executives with debate host CNN have said they'll squeeze in an extra podium for the still-deciding Joe Biden if the vice president files last-minute paperwork for a 2016 presidential bid before the debate begins.

CNN reported recently that the vice president was likely to skip the opening debate. Still, the Biden question mark adds drama, said Grant Woodard, an Iowa political operative and lawyer.

"If he is there," Woodard said, "it will be one hell of a show."

The debate comes as Sanders has closed the polling gap on Clinton in Iowa, where party caucuses kick off the nation's presidential voting, and overtaken her in New Hampshire, home of the first primary.

Here are six things to watch for:

1. Steam from the Hillary grilling

If the CNN debate moderators treat this as their chance to grill Clinton on live TV instead of carrying out an actual debate where other candidates are allotted plenty of time to make their case, "Democrats will likely be frustrated," said Pat Rynard, a former Democratic campaign staffer from Iowa.

2. The Biden shadow

Even if he's not on the stage, "Joe is a real part of the debate," said Democrat Patty Judge, a former Iowa lieutenant governor.

"Sadly," added Rynard, "in terms of the media narrative, nothing in the debate may matter if Biden announces his intentions the next day and wipes out all the coverage. Hopefully that doesn't happen, but it's near when Biden has to make a decision for ballot purposes."

3. Sanders' fidelity to fixed talking points

The liberal messenger could miss an opportunity if he expounds only a dry, policy-heavy message, Democrats said.

"He really refuses to deviate much from his economic inequality shtick on the campaign trail — which, to be fair, is a very powerful message that has gotten him far," said Rynard, who writes about presidential politics on the website Iowa Starting Line. "(But) debates tend to favor interaction and candidates quick on their toes who can give punchy responses."

4. Two debates in one

One debate will likely be a policy contest between Clinton and Sanders, both of whom have declined to stray into personal attacks, observers said.

"She will continue to move herself to the left in order to appeal to undecideds and to those who are leaning to Sanders but not firmly in his camp," Judge said of Clinton. "She will also try to continue to distance herself from the Obama administration to give herself room to take on Biden if he gets into the race."

The second debate could feature hard swings from the low-polling contenders, especially O'Malley, who has gotten increasingly personal in drawing contrasts with Clinton.

Watch for gun control, trade, banks and foreign policy to take center stage, said Michael Cheney, a professor of communication and economics at the University of Illinois at Springfield.

5. O'Malley's moment?

Many Democrats worry that Sanders' "socialist" label and Clinton's struggles with her email controversy would badly hinder them in the general election, Rynard said.

O'Malley has run a serious campaign and impressed Democrats who go see him. But he barely attracts national media coverage, and many voters haven't noticed him yet.

Cutter said: "This is the last best chance for Martin O'Malley."

O'Malley needs to pull votes from Sanders, she said. "If he doesn't distinguish himself as the person more likely to achieve results for a progressive agenda, rather than just a protest," Cutter said, "then he's out."

6. The invisible Democrats

It's now or never for Webb and Chafee, neither of whom do any real campaigning, Rynard said.

"At this point, they're just taking up space," he said.

Democrats said they're hesitant to take either candidate seriously when even low-polling GOP candidates such as Rick Santorum, Bobby Jindal and Lindsey Grahamthrow energy into reaching out to early state voters.

But debates are fertile ground for earning a bump in the polls, strategists noted.

"The best debaters," Sefl said, "are those who don't look like they rehearsed their one-liners thousands of times, and who know how to demonstrate command of the issues without being the annoying kid from class who always raised their hand to every question."