Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.) is set to give a campaign-defining address on democratic socialism and expand on his national security platform at Georgetown University on Thursday.

The presidential candidate will deliver the 2 p.m. address as he seeks to regain momentum in the Democratic primary against Hillary Clinton Hillary Diane Rodham ClintonButtigieg stands in as Pence for Harris's debate practice Senate GOP sees early Supreme Court vote as political booster shot Poll: 51 percent of voters want to abolish the electoral college MORE and prove that he is electable even with the “democratic socialist” label.

Since Sanders burst onto the scene with rising poll numbers, Clinton has gained the upper hand and holds a comfortable lead in national and most statewide polls — except for of New Hampshire, where she leads by only 3 points, according to the RealClearPolitics average of polls.

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Sanders’s team has long sought a way to clarify the independent Vermont senator’s views as a democratic socialist, which is often conflated with socialism.

The speech will be the “definitive explanation” on Sanders’s identity as a democratic socialist, an aide told The Hill.

It is fair, the aide added, to compare the speech to then-Sen. Barack Obama Barack Hussein ObamaMichelle Obama and Jennifer Lopez exchange Ginsburg memories Pence defends Trump's 'obligation' to nominate new Supreme Court justice The militia menace MORE’s speech on race in 2008, in which he confronted both that issue and the controversial remarks of his former reverend.

Thursday’s speech “is going to be another major moment in his campaign,” the aide said of Sanders.

While the speech has been in the works for some time, Sanders has added a foreign policy element in light of the terror attacks in Paris last week. He plans to focus on both a strategy to defeat the Islamic State in Iraq and Syria and to keep the world safer in the longer term.

Sanders has focused his campaign largely on domestic issues, often speaking about fixing income inequality and boosting the middle class, but has had to shift his emphasis as foreign policy dominated other issue this week.

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Mo Elleithee, executive director of the new Georgetown University Institute of Politics and Public Service, where Sanders will speak, called the address “one of those defining moments in a presidential campaign” in a statement announcing the event.

“It’s one of those things he and the campaign probably recognized that they need to do, as it is one of the big questions that hangs out there,” Elleithee told The Hill.

“It’s smart of him to take it head-on, something he could have done sooner, but now is as good of a time as any to address it and explain to people what it means and what his world view is,” said Elleithee, a former spokesman for Clinton’s 2008 presidential campaign and the Democratic National Committee.

“At the end of the day, they are banking on the fact that people will get past the label if they feel comfortable with what it is he wants to do.”

Sanders attempted to explicitly address the issue of democratic socialism during the first Democratic debate, where he made a compassionate appeal about the label.

“We are going to win because we are going to explain what democratic socialism is,” he said.

“What democratic socialism is about is saying that it is immoral and wrong to say that the top one-tenth of 1 percent in this country own almost as much wealth as the bottom 90 percent,” Sanders said.

He added that he doesn’t consider himself part of the “casino capitalist process” and noted the success of democratic socialist policies in countries like Denmark.

That opened him up to criticism from Clinton, who noted that America is different than Denmark.

The Sanders aide couldn’t say whether the issue will still continue to be “a point of contention” on the trail but added that the campaign isn’t worried.

“We live in a rigged economy kept in place by a corrupt campaign finance system,” the aide said.

“So the fact that the way the senator views democratic socialism is through that lens. … That’s actually a strength of his, not a weakness as some folks in the party might characterize it.”

This story was updated at 6:57 p.m.