The Democrats’ dramatic, leftward turn is proof of how “sick” the party has become and why it is “the greatest threat to the constitution,” according to Fox News Channel’s Mark Levin.

Levin, a best-selling author whose daily broadcast is heard by more than 10 million listeners on nearly 400 stations and who also hosts Fox News’ “Life, Liberty & Levin,” delivered the explosive diagnosis during “Hannity” on Thursday night.

After Sean Hannity mentioned some of the recent pushes by Dems to scrap the Electoral College and stack the Supreme Court, Levin launched his attack.

“The greatest threat to our constitution and economic system isn’t any foreign power, it’s the Democrat party,” he said. “It’s the leftists within the Democrat party, because they use our liberty and our constitution to destroy our liberty and our constitution, and they’re very good at it. Look at this, you named some of them.”

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Levin then turned his attention to Democratic presidential candidates who declined invitations to a key pro-Israel policy group's conference next week, an annual meeting that has usually been a must-attend meeting for members of both parties, in what some see as a further sign of the party's growing disdain for the Jewish state.

Sens. Bernie Sanders, Kamala Harris, Elizabeth Warren, former Rep. Beto O’Rourke and many others have said they won’t be attending the American Israel Public Affairs Committee's annual Policy (AIPAC) conference, a move that coincides with a moneyed progressive advocacy group’s call to boycott the event.

“This is a sick party,” Levin said. “These are sick people running for president of the United States. There is no other explanation for this.”

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MoveOn.org, a group that spent around $3.5 million in the 2018 midterm elections, called on the 2020 Democratic candidates to skip the conference, even though in the past all presidential candidates viewed the AIPAC conference as a crucial campaign stop.

The three-day conference this year will be headlined by Israeli Prime Minister Benjamin Netanyahu, Vice President Mike Pence, Senate Majority Leader Chuck Schumer, Secretary of State Mike Pompeo, House Speaker Nancy Pelosi, New York City Mayor Bill de Blasio, and Democratic House Majority Leader Steny Hoyer.

So far no Democrats who are officially running for president have issued a statement confirming their attendance at the conference.

Sanders’ aide Josh Orton told media outlets that the leading candidate among the Democrats won’t be attending because “he’s concerned about the platform AIPAC is providing for leaders who have expressed bigotry and oppose a two-state solution” in the Israeli-Palestinian conflict.

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Other candidates such as Kamala Harris or Elizabeth Warren, meanwhile, confirmed that they don't plan to attend the conference, but provided no explanation for their decisions.

Harris addressed the AIPAC in 2017, saying it was “an honor” to speak there and praised the group’s leadership. “And I'm proud to say and be among the many voices represented here, the California delegation is the largest and hopefully the loudest. There you go,” she said.

O’Rourke criticized the embattled Israeli prime minister during a campaign stop earlier this week, saying Netanyahu “has openly sided with racists.”

“Right now, we don’t have the best-negotiating partners on either side. We have a prime minister in Israel who has openly sided with racists,” he charged.

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Other Democratic candidates who won’t be attending the conference are Julian Castro, Pete Buttigieg, and Rep. John Delaney, though the latter politician said he’s unable to attend due to scheduling conflicts.

AIPAC is a non-partisan organization that seeks to foster the relationship between the U.S. and Israel. The group, despite misleading portrayals on the far-left, supports a two-state solution and doesn’t endorse nor donate to political candidates.

Fox News' Lukas Mikelionis contributed to this report