Former Sen. Joe Lieberman (I-Conn.) is urging voters in the general election to vote for Rep. Joseph Crowley (D-N.Y.) instead of Democratic nominee Alexandria Ocasio-Cortez, who upset him in the party primary.

"Alexandria Ocasio-Cortez’s surprise primary victory over Rep. Joe Crowley Joseph (Joe) CrowleyHillicon Valley: Election officials prepare for new Russian interference battle | 'Markeyverse' of online fans helps take down a Kennedy | GOP senators unveil bill to update tech liability protections 'Markeyverse' of online fans helps take down a Kennedy The Hill's Campaign Report: Trump visits Kenosha | Primary day in Massachusetts | GOP eyes Minnesota as a battleground MORE seems likely to hurt Congress, America and the Democratic Party. It doesn’t have to," Lieberman wrote in an op-ed published Tuesday in The Wall Street Journal.

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"Because the policies Ms. Ocasio-Cortez advocates are so far from the mainstream, her election in November would make it harder for Congress to stop fighting and start fixing problems."

Lieberman noted that Crowley's name will still be on the ballot as the nominee of the Working Families Party.

“Thanks to a small percentage of primary votes, all of the people of New York’s 14th Congressional District stand to lose a very effective representative in Washington,” Lieberman wrote. “Fortunately, Joe Crowley and the voters in his district can prevent this damage.”

Ocasio-Cortez defeated Crowley by 15 percentage points in the June 28 Democratic primary.

Her stunning upset rattled the Democratic establishment in Washington, D.C.

The two rivals also feuded on Thursday, with Ocasio-Cortez accusing Crowley of mounting a third-party challenge. She said he had failed to make time for a concession call and was refusing take his name off the ballot for the Working Families Party.

Crowley responded that he had made his support for her “clear” and that “Democrats need to come together.”

He also claimed that his name could only be removed from the ballot if he moves out of New York, is convicted of a crime, accepts a nomination for another office in a different district, or dies.

In his op-ed, Lieberman recounted how he faced a similar, “difficult” choice when he lost the Democratic nomination for the Senate in 2006 to Ned Lamont. But Lieberman eventually won reelection in the general as an independent candidate.

“I ran as an independent because I wanted all the voters to decide whether I deserved to continue to serve them in the Senate,” Lieberman wrote. “It was a risk, but I concluded it was worth it to know that I had taken my fight for the kind of government I believed in as far as I possibly could.”

Lieberman, viewed by many as an independent voice in politics, continued to caucus with Democrats, but endorsed Sen. John McCain John Sidney McCainThe Memo: Trump's strengths complicate election picture Mark Kelly: Arizona Senate race winner should be sworn in 'promptly' Cindy McCain: Trump allegedly calling war dead 'losers' was 'pretty much' last straw before Biden endorsement MORE’s (R-Ariz.) presidential run at the 2008 Republican National Convention.

The former 2000 Democratic vice presidential nominee also attacked Ocasio-Cortez’s policies for being “more socialist than Democratic.”

“She has received the most attention for calling to 'Abolish ICE,' Immigration and Customs Enforcement,” he wrote. “This makes no sense unless you no longer want any rules on immigration or customs to be enforced.”

Ocasio-Cortez's campaign declined to comment to The Hill.