LAS VEGAS — Hillary Clinton and Donald Trump meet for a final debate in Las Vegas that is their last opportunity to reach an audience of millions of voters. They appear to have far different goals as they make a closing argument to America.

The real estate billionaire is the underdog in nearly every single national poll conducted in the past week, a deficit that could translate into a crushing defeat in the Electoral College, with surveys showing traditionally Republican states like Arizona now in play.

Trump will be on offense, trying to drag Clinton into battles over everything from her use of a private email server to her husband’s history of philandering and the latest WikiLeaks hacked emails that have proven embarrassing for her campaign. He’s also amplifying his argument that the election is being “rigged,” something he’s sure to be asked to defend during the forum at the University of Nevada, Las Vegas.

For her part, Clinton is looking to maximize her appeal to independent and soft Republican voters. If polls are accurate that she’s the prohibitive winner, her next challenge will be to unify the country behind her.

“This is her last big opportunity to be in front of a big national audience and make her case,” Clinton communications director Jennifer Palmieri told reporters. “If he chooses to continue to embrace his strategy of a scorched-earth campaign and bringing that to the debate stage, she’ll be prepared to handle that,” said Palmieri.

Her goal is not to be dragged into fights that further depress enthusiasm among her base voters and turn off swing voters. Even if Clinton is ahead in the polls, the Republican-controlled House is unlikely to switch hands and she is unlikely to have a filibuster-proof majority in the Senate.

Unifying the nation looks increasingly difficult in an election that will go down in history as among the nastiest and most personal. Sen. John McCain, R-Ariz., has already been on record saying he’d oppose whomever she nominates to the Supreme Court, comments he later softened. Yet it underscores the challenge a President Hillary Clinton is likely to face in governing.

That means pulling punches that may alienate swing voters, while focusing on the areas of potential compromise with Congress.

When it comes to WikiLeaks, while there is no single smoking gun, collectively the hacked messages risk painting a cynical view of her campaign that could endure beyond the election. Clinton must have an effective rejoinder that doesn’t revolve solely around blaming the Russians.

Among the most politically damaging exchanges may be an excerpt of a 2013 Clinton speech to a Brazilian bank in which she said her “dream” is “a hemispheric common market, with open trade and open borders.” She is sure to be asked to explain her comments by the moderator, Fox News’s Chris Wallace.

Even as Trump goes on the offense against Clinton, he enters this final debate amid strong evidence that her efforts to paint him as temperamentally unfit for the presidency have been successful. According to the latest Fox News poll of likely voters, Clinton’s national lead is 6 points, or outside the margin of error.

Their numbers on temperament and judgment are lopsided. Sixty-one percent of voters say Clinton has the temperament to serve effectively as president, while the same percentage think Trump doesn’t.

By a 7-point margin, voters say Clinton has the judgment to serve (53%-46%). It’s the opposite for Trump, with a 23-point margin saying they believe he lacks the judgment (37%-60%).

That increases the need for Trump to avoid angry outbursts that marked the last forum. The New York businessman has never held public office, and his lack of familiarity with the challenges of the job have become apparent. One of the scheduled debate topics is "fitness to be president," and Trump needs to rise to that challenge.

Trump needs to get beyond attacking Clinton (and her husband). He needs to talk about what he would do as president and what kind of vision he would bring to the presidency. Look for Trump to talk more about issues, such as his new proposed political ethics reforms. Another scheduled debate topic should be in Trump's wheelhouse: immigration, which didn't surface during the first two sessions with Clinton

Trump is signaling he’ll play tough, including again inviting guests intended to rattle Clinton. This time he’s bringing President Obama’s half brother, Malik Obama, and the mother of a slain service member in Benghazi, Libya, as guests.

Clinton has invited billionaire Mark Cuban and Meg Whitman, the former finance chair of Mitt Romney’s presidential campaign and the 2010 Republican nominee for governor of California.