Washington (CNN) The shadow boxing that Hillary Clinton and Bernie Sanders have played at for months -- they've barely mentioned each other on the campaign trail -- will give way to more direct jabs Tuesday night.

That's when the two rivals line up on stage at the first Democratic debate of the 2016 campaign, sponsored by CNN and Facebook. The encounter will provide a crucial opportunity for Clinton and Sanders -- the leading Democratic contenders -- to contrast their personalities, experience and approach to the key issues in the campaign.

Though Clinton and Sanders have rarely mentioned each other's names, they are clearly reacting to each other and their rival's potential weaknesses. Sanders took aim at Clinton's Wall Street record and Iraq vote over the weekend; she put him on the defensive on guns and his poor standing with minority voters.

Until now, they have each had good reason for avoiding full contact with the other. Clinton hasn't wanted to elevate Sanders and his surprisingly strong poll numbers, while Sanders has wanted to maintain his untraditional, above-the-fray image.

On Tuesday, that calculus will change. And the distinctions they've subtly staked out on a range of issues are only likely to grow sharper.

Prepping positions for first debate

In the weeks leading up to the debate in Las Vegas, the two Democrats have been carefully finessing their political positions in relation to each other and their party's wide coalition, offering clues about how they will spar Tuesday night.

Sanders has been signaling he will try to strike a contrast with Clinton on reining in Wall Street and on her record of support for military interventions overseas. The former secretary of state, meanwhile, is under pressure to prove to progressives who have flocked to Sanders that she genuinely cares about the middle class. She's expected to highlight her differences with her rival on gun control and to demonstrate the broad support she has among minority voters -- a key sector of the Democratic coalition where Sanders is struggling.

As he limbered up for their clash, Sanders threw down the gauntlet on the Iraq War -- a thrust that Clinton has struggled to counter in the past -- hinting that she has hawkish views that are out of step with the majority of Democratic voters.

His campaign issued a statement reminding voters that he, then a member of the House of Representatives, voted against authorizing the Iraq war in late 2002. At the time he argued that the conflict would destabilize the Middle East, kill large numbers of Americans and Iraqi civilians and hamper the war on terror against al Qaeda.

Photos: Hillary Clinton's life in the spotlight Photos: Hillary Clinton's life in the spotlight Hillary Clinton accepts the Democratic Party's nomination for president at the Democratic National Convention in Philadelphia on July 28, 2016. The former first lady, U.S. senator and secretary of state was the first woman to lead the presidential ticket of a major political party. Hide Caption 1 of 43 Photos: Hillary Clinton's life in the spotlight Before marrying Bill Clinton, she was Hillary Rodham. Here she attends Wellesley College in Massachusetts. Her commencement speech at Wellesley's graduation ceremony in 1969 attracted national attention. After graduating, she attended Yale Law School. Hide Caption 2 of 43 Photos: Hillary Clinton's life in the spotlight Rodham was a lawyer on the House Judiciary Committee, whose work led to impeachment charges against President Richard Nixon in 1974. Hide Caption 3 of 43 Photos: Hillary Clinton's life in the spotlight In 1975, Rodham married Bill Clinton, whom she met at Yale Law School. He became the governor of Arkansas in 1978. In 1980, the couple had a daughter, Chelsea. Hide Caption 4 of 43 Photos: Hillary Clinton's life in the spotlight Arkansas' first lady, now using the name Hillary Rodham Clinton, wears her inaugural ball gown in 1985. Hide Caption 5 of 43 Photos: Hillary Clinton's life in the spotlight The Clintons celebrate Bill's inauguration in Little Rock, Arkansas, in 1991. He was governor from 1983 to 1992, when he was elected President. Hide Caption 6 of 43 Photos: Hillary Clinton's life in the spotlight Bill Clinton comforts his wife on the set of "60 Minutes" after a stage light broke loose from the ceiling and knocked her down in January 1992. Hide Caption 7 of 43 Photos: Hillary Clinton's life in the spotlight In June 1992, Clinton uses a sewing machine designed to eliminate back and wrist strain. She had just given a speech at a convention of the International Ladies' Garment Workers Union. Hide Caption 8 of 43 Photos: Hillary Clinton's life in the spotlight During the 1992 presidential campaign, Clinton jokes with her husband's running mate, Al Gore, and Gore's wife, Tipper, aboard a campaign bus. Hide Caption 9 of 43 Photos: Hillary Clinton's life in the spotlight Clinton accompanies her husband as he takes the oath of office in January 1993. Hide Caption 10 of 43 Photos: Hillary Clinton's life in the spotlight The Clintons share a laugh on Capitol Hill in 1993. Hide Caption 11 of 43 Photos: Hillary Clinton's life in the spotlight Clinton unveils the renovated Blue Room of the White House in 1995. Hide Caption 12 of 43 Photos: Hillary Clinton's life in the spotlight Clinton waves to the media in January 1996 as she arrives for an appearance before a grand jury in Washington. The first lady was subpoenaed to testify as a witness in the investigation of the Whitewater land deal in Arkansas. The Clintons' business investment was investigated, but ultimately they were cleared of any wrongdoing. Hide Caption 13 of 43 Photos: Hillary Clinton's life in the spotlight The Clintons hug as Bill is sworn in for a second term as President. Hide Caption 14 of 43 Photos: Hillary Clinton's life in the spotlight The first lady holds up a Grammy Award, which she won for her audiobook "It Takes a Village" in 1997. Hide Caption 15 of 43 Photos: Hillary Clinton's life in the spotlight The Clintons dance on a beach in the U.S. Virgin Islands in January 1998. Later that month, Bill Clinton was accused of having a sexual relationship with former White House intern Monica Lewinsky. Hide Caption 16 of 43 Photos: Hillary Clinton's life in the spotlight Clinton looks on as her husband discusses the Monica Lewinsky scandal in the Roosevelt Room of the White House on January 26, 1998. Clinton declared, "I did not have sexual relations with that woman." In August of that year, Clinton testified before a grand jury and admitted to having "inappropriate intimate contact" with Lewinsky, but he said it did not constitute sexual relations because they had not had intercourse. He was impeached in December on charges of perjury and obstruction of justice. Hide Caption 17 of 43 Photos: Hillary Clinton's life in the spotlight The first family walks with their dog, Buddy, as they leave the White House for a vacation in August 1998. Hide Caption 18 of 43 Photos: Hillary Clinton's life in the spotlight President Clinton makes a statement at the White House in December 1998, thanking members of Congress who voted against his impeachment. The Senate trial ended with an acquittal in February 1999. Hide Caption 19 of 43 Photos: Hillary Clinton's life in the spotlight Clinton announces in February 2000 that she will seek the U.S. Senate seat in New York. She was elected later that year. Hide Caption 20 of 43 Photos: Hillary Clinton's life in the spotlight Clinton makes her first appearance on the Senate Environment and Natural Resources Committee. Hide Caption 21 of 43 Photos: Hillary Clinton's life in the spotlight Sen. Clinton comforts Maren Sarkarat, a woman who lost her husband in the September 11 terrorist attacks, during a ground-zero memorial in October 2001. Hide Caption 22 of 43 Photos: Hillary Clinton's life in the spotlight Clinton holds up her book "Living History" before a signing in Auburn Hills, Michigan, in 2003. Hide Caption 23 of 43 Photos: Hillary Clinton's life in the spotlight Clinton and another presidential hopeful, U.S. Sen. Barack Obama, applaud at the start of a Democratic debate in 2007. Hide Caption 24 of 43 Photos: Hillary Clinton's life in the spotlight Obama and Clinton talk on the plane on their way to a rally in Unity, New Hampshire, in June 2008. She had recently ended her presidential campaign and endorsed Obama. Hide Caption 25 of 43 Photos: Hillary Clinton's life in the spotlight Obama is flanked by Clinton and Vice President-elect Joe Biden at a news conference in Chicago in December 2008. He had designated Clinton to be his secretary of state. Hide Caption 26 of 43 Photos: Hillary Clinton's life in the spotlight Clinton, as secretary of state, greets Russian Prime Minister Vladimir Putin during a meeting just outside Moscow in March 2010. Hide Caption 27 of 43 Photos: Hillary Clinton's life in the spotlight The Clintons pose on the day of Chelsea's wedding to Marc Mezvinsky in July 2010. Hide Caption 28 of 43 Photos: Hillary Clinton's life in the spotlight In this photo provided by the White House, Obama, Clinton, Biden and other members of the national security team receive an update on the mission against Osama bin Laden in May 2011. Hide Caption 29 of 43 Photos: Hillary Clinton's life in the spotlight Clinton checks her Blackberry inside a military plane after leaving Malta in October 2011. In 2015, The New York Times reported that Clinton exclusively used a personal email account during her time as secretary of state. The account, fed through its own server, raises security and preservation concerns. Clinton later said she used a private domain out of "convenience," but admits in retrospect "it would have been better" to use multiple emails. Hide Caption 30 of 43 Photos: Hillary Clinton's life in the spotlight Clinton arrives for a group photo before a forum with the Gulf Cooperation Council in March 2012. The forum was held in Riyadh, Saudi Arabia. Hide Caption 31 of 43 Photos: Hillary Clinton's life in the spotlight Obama and Clinton bow during the transfer-of-remains ceremony marking the return of four Americans, including U.S. Ambassador Christopher Stevens, who were killed in Benghazi, Libya, in September 2012. Hide Caption 32 of 43 Photos: Hillary Clinton's life in the spotlight Clinton ducks after a woman threw a shoe at her while she was delivering remarks at a recycling trade conference in Las Vegas in 2014. Hide Caption 33 of 43 Photos: Hillary Clinton's life in the spotlight Clinton, now running for President again, performs with Jimmy Fallon during a "Tonight Show" skit in September 2015. Hide Caption 34 of 43 Photos: Hillary Clinton's life in the spotlight Clinton testifies about the Benghazi attack during a House committee meeting in October 2015. "I would imagine I have thought more about what happened than all of you put together," she said during the 11-hour hearing. "I have lost more sleep than all of you put together. I have been wracking my brain about what more could have been done or should have been done." Months earlier, Clinton had acknowledged a "systemic breakdown" as cited by an Accountability Review Board, and she said that her department was taking additional steps to increase security at U.S. diplomatic facilities. Hide Caption 35 of 43 Photos: Hillary Clinton's life in the spotlight U.S. Sen. Bernie Sanders shares a lighthearted moment with Clinton during a Democratic presidential debate in October 2015. It came after Sanders gave his take on the Clinton email scandal. "The American people are sick and tired of hearing about the damn emails," Sanders said. "Enough of the emails. Let's talk about the real issues facing the United States of America." Hide Caption 36 of 43 Photos: Hillary Clinton's life in the spotlight Clinton is reflected in a teleprompter during a campaign rally in Alexandria, Virginia, in October 2015. Hide Caption 37 of 43 Photos: Hillary Clinton's life in the spotlight Clinton walks on her stage with her family after winning the New York primary in April. Hide Caption 38 of 43 Photos: Hillary Clinton's life in the spotlight After Clinton became the Democratic Party's presumptive nominee, this photo was posted to her official Twitter account. "To every little girl who dreams big: Yes, you can be anything you want -- even president," Clinton said. "Tonight is for you." Hide Caption 39 of 43 Photos: Hillary Clinton's life in the spotlight Obama hugs Clinton after he gave a speech at the Democratic National Convention in Philadelphia. The president said Clinton was ready to be commander in chief. "For four years, I had a front-row seat to her intelligence, her judgment and her discipline," he said, referring to her stint as his secretary of state. Hide Caption 40 of 43 Photos: Hillary Clinton's life in the spotlight Clinton arrives at a 9/11 commemoration ceremony in New York on September 11. Clinton, who was diagnosed with pneumonia two days before, left early after feeling ill. A video appeared to show her stumble as Secret Service agents helped her into a van. Hide Caption 41 of 43 Photos: Hillary Clinton's life in the spotlight Clinton addresses a campaign rally in Cleveland on November 6, two days before Election Day. She went on to lose Ohio -- and the election -- to her Republican opponent, Donald Trump. Hide Caption 42 of 43 Photos: Hillary Clinton's life in the spotlight After conceding the presidency to Trump in a phone call earlier, Clinton addresses supporters and campaign workers in New York on Wednesday, November 9. Her defeat marked a stunning end to a campaign that appeared poised to make her the first woman elected US president. Hide Caption 43 of 43

The statement did not once mention Clinton -- but it did not have to. The then-New York senator did vote to authorize the Iraq war, and that vote was one of her greatest vulnerabilities in the 2008 Democratic campaign against Obama, who also opposed the war.

The Sanders statement raised the possibility that Clinton's vote could haunt her for a second presidential campaign.

"Democrats are no more fond of the Iraq war now than they were back then. That could be a problem," Peter Beinart, a foreign policy expert and CNN contributor, said Monday. He added that another Democratic candidate, former Virginia senator and Vietnam war veteran Jim Webb, who was also against the war, could double-team with Sanders to cause trouble for Clinton on the issue.

Sanders has also been staking out territory to Clinton's left on Syria. The former secretary of state recently distanced herself from Obama's much-criticized policy on the vicious civil war by calling for a no-fly zone to be set up to shield refugees.

Sanders issued a statement earlier this month pointing out that he opposes such an idea, warning that it could "get us more deeply involved in that horrible civil war and lead to a never ending entanglement in that region."

The statement appeared to be a clear appeal to Democrats who share Obama's antipathy toward getting the United States entangled in another Middle Eastern conflict and who are wary of Clinton's more activist instincts on foreign policy.

Attacks on Wall Street

Sanders is not alone in seeing Clinton's foreign policy record as a vulnerability. Another Democratic candidate, former Maryland Gov. Martin O'Malley, also picked up on her Syria position Sunday -- saying on CNN's "State of the Union" that a no-fly zone was not advisable and warning that the former secretary of state was "always quick for the military intervention," apparently referring to her previous support for military action in nations such as Iraq and Libya.

Another area where Sanders seems more in tune with the progressive Democratic base is on Wall Street, especially since he has raised most of his money from small donors -- unlike the former secretary of state, who has been relying on big budget fund-raising events with rich contributors. Even with his small-donor focus, Sanders is nearly neck-and-neck in the fund-raising race with Clinton.

Clinton has made strenuous attempts to connect with what her campaign has called "regular" Americans, stressing the need to raise up the middle class to feel the benefits of the economic recovery. But Sanders has said that she hasn't done enough, an argument he may expand upon on the debate stage.

"People will have to contrast my consistency and my willingness to stand up to Wall Street and corporations with the secretary," Sanders said on NBC's "Meet the Press" on Sunday.

The Vermont senator also will likely draw an implied contrast with Clinton on two other issues -- the Trans-Pacific Partnership trade pact the United States and 11 other nations reached this month and the Keystone XL pipeline designed to carry oil from Canada's tar sands across the United States.

Clinton now says she is a 'no' on both issues, but she took months to get there -- despite fervent opposition to both projects from the left flank of the Democratic Party.

"I am glad that she has reached that conclusion," said Sanders in Washington last week when asked about Clinton's opposition to a trade agreement she championed repeatedly as secretary of state. "This is a conclusion that I reached from day one."

Yet Sanders is not alone in curating the battlefield for the Democratic debate. Clinton, while getting in line with progressive Democratic positions on big issues, has also been preparing to strike key contrasts with Sanders.

Differences on gun control

Guns are one policy issue where Sanders is not completely in sync with the Democratic base, so Clinton is likely to exploit it on Tuesday night.

She has been promising a forthright effort to enact new gun control laws after a string of recent mass shootings. It partly seems to be an attempt to focus attention her rival's record on guns, which recently saw him express his openness to reforms that would hold gun manufacturers liable for crimes committed with their weapons.

Clinton has also spent the runup to the debate cementing her links to key voting blocs of the Democratic coalition -- especially in sectors of the party where Sanders is weak. She can point to broad appeal in the party, which could be key to eventually blunting the challenge from Sanders after early-voting contests in the less diverse states of Iowa and New Hampshire where he is strong.

In recent weeks, Clinton has met representatives of the Black Lives Matter movement and has even criticized Obama for not going far enough in changing immigration laws.

"Hillary has done a lot of work leading up to this debate that has pretty much gone unnoticed," Patti Solis Doyle, Clinton's 2008 campaign manager, said on CNN on Monday.

"She's rolled out Latinos for Hillary, she has rolled out Women for Hillary, she has met with the leadership of Black Lives Matter, she has checked a lot of boxes walking into this debate," she noted. "I think she is going to display tomorrow night (Tuesday) her vast support among this coalition."

The challenge that Sanders faces reaching out to minority voters, who are a vital part of the Democratic Party voting bloc, was underscored by a new CNN poll Monday finding that only 1% of nonwhite voters in the important early voting state of South Carolina favor him.

That is a showing that Sanders must improve on if he is to come from behind and beat Clinton for the nomination.