Hillary Clinton, Bernie Sanders and rest of 2016 Dems set for first debate

Hillary Clinton and Bernie Sanders, the two candidates atop national and early state polls, have their first chance Tuesday to duel in person on trade, income inequality and other top issues of Democratic voters at the party's first debate in Las Vegas.

In recent weeks, Clinton has crept closer to Sanders on a number of more liberal policies. She came out in opposition to both the Keystone XL pipeline and the Trans-Pacific trade deal — which she previously supported — as she tries to neutralize an unexpectedly potent challenge from the self-described democratic socialist Vermont senator.

The debate, the first of six for Democrats, will also feature former Maryland governor Martin O'Malley, former Virginia senator Jim Webb and former Rhode Island governor Lincoln Chafee.

There are still big differences between Clinton and Sanders, and they’ll come into focus during the candidate forum. Sanders wants to break up the big banks, while Clinton would penalize bankers who violate the law. He would also raise the minimum wage higher than she would, to $15 an hour, and expand health care coverage through a major Medicare expansion. She says she wants to improve the Affordable Care Act. Clinton also voted for the Iraq War as a senator, while Sanders opposed it while in the House.

Yet Clinton’s greatest challenge is probably not on any specific issue.

Prep for the polls: See who is running for president and compare where they stand on key issues in our Voter Guide

Rather, she'll need to convince Democratic voters that her recent leftward drift is genuine and not just political opportunism amid the heat of a primary battle.

Bernie Sanders' success may be pushing Hillary Clinton to the left

Six things to watch for in the Las Vegas Democratic debate

In an appearance Sunday on NBC’s Meet the Press, Sanders previewed his case against Clinton, the front-runner. "People have to contrast my consistency and my willingness to stand up to Wall Street and corporations, big corporations, with the secretary,’’ he said.

"It is going to be tough to walk away from her role’’ as the nation’s former top diplomat on issues like Keystone and trade, said Bill Buck, a Democratic strategist who is unaligned with a candidate. "She needs to walk a fine line to avoid a mistake.’’

As for the the other debate participants, O’Malley may have the most at stake, with polls showing him stuck below 1%. A breakout moment may be his only hope of gaining the traction needed to secure the money and endorsements necessary to continue his bid.

For Clinton, the debate is also a chance to shift the focus away  from her use of a private email server while she served as secretary of State, a controversy that’s dragged down her poll ratings, and on to her policy proposals. A weak or strong performance might also tip the hand of Vice President Biden, who is still mulling a decision on whether to enter the race.

Clinton is trying to demonstrate her commitment to progressives without alienating the wealthy donors her campaign will rely on far more than Sanders, whose financial support comes mostly from small, Internet-based donors.

For Sanders, the challenge is to convert his populist fire on the stump into a more personal and engaging approach that draws contrasts with Clinton’s past positions without appearing to directly attack her.

The one issue on which he may find himself on defense is guns. While Sanders now supports expanding background checks, he has a long record of opposing gun control, including the 1994 Brady Law that established mandatory background checks.

"I would push Sanders hard on guns,’’ said Buck. "It’s a bigger liability in the primaries than the Iraq War vote.’’

Debate: What Clinton, Sanders and the rest need to do

How to watch the Las Vegas Democratic debate

The debate location, Nevada, is a showcase of sorts for an argument Clinton aides make that the Sanders threat is overblown.

Once the battle moves from overwhelmingly older and white Iowa and New Hampshire, they say, her grip on the nomination will tighten. In Nevada, the first early-voting state with a large Latino population, Clinton has a 16-point lead over Sanders, according to a recent CNN/ORC poll.

The advantage widens to 22 points without Biden in the race. Her lead in South Carolina, the first Southern voting primary state, is even wider, at 25 points over Biden and 31 points over Sanders.

Until recently, Clinton has behaved as a prohibitive front-runner, largely ignoring Sanders.

Then Sanders came within $2 million of Clinton’s fundraising totals over the past quarter and has continued to draw large crowds. Even if he’s unlikely to secure the nomination, he’s already succeeded in pushing Clinton leftward on many issues in a race that, several months ago, seemed like it might not be much of one.

For their part, Republicans want to keep Democrats, and specifically Sanders’ supporters, focused on Clinton’s emails.

In an ad released ahead of the debate, the Republican National Committee highlights Clinton’s previous comments that she "did not email classified material to anyone.’’ As the State Department and other agencies review her emails, officials have decided to classify hundreds of the emails after the fact.

Follow @HeidiPrzybyla on Twitter