Livni said during the joint press conference that "Peretz will prove he can stand up for his beliefs, like he did with the Iron Dome... We are acting on the belief that it is possible to replace this government, and finally bring hope to the citizens of Israel."
Explaining the reasons behind his decision to leave, Peretz said that he has been offering Shelly Yachimovich his help and support ever since she was elected as the leader of the Labor Party, but "she always rejected my outstretched hand."
In his speech Peretz urged Likud supporters to reconsider their choice ahead of the national elections.
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"(Likud voters) know that Likud Beiteinu isn't leading them anywhere but towards extremism and confrontations with the entire world," he said. "(…) With your help we won't allow this historic opportunity to pass us by and will establish a government headed by Livni."
Peretz, who relinquished his position at the Knesset, is to be replaced in the role by former MK Yoram Marciano. The businessman was the next in line on the Labor list in the previous elections. He is to take over the position until January.
'Relieved to part ways'In a statement released in response to Peretz's announcement, the Labor Party suggested the step was not unwelcome.
"We are relieved to part ways with a man who tried to undermine the party at the height of its success, but failed," the statement read. "Peretz's decision to join Livni won't hurt the Labor Party one bit; in fact, it will empower it and allow it to work... without being subverted from within."
The party added that Livni has reached "a new political low," accusing her of "collecting 'refugees' in a manner completely devoid of ideology."
Peretz's former fellow party members appeared to be caught off guard by the announcement.
"I'm in complete shock," said Knesset Member Eitan Cabel, who noted he learned of the decision during Thursday's press conference. "It's a difficult feeling because we were partners and friends. It's a hard blow personally."
'Hatred from within'
Tension between Peretz and Yachimovich has been mounting for weeks. Peretz has been unsuccessfully urging Yachimovich to publically declare that she will not join a coalition headed by Prime Minister Benjamin Netanyahu and Foreign Minister Avigdor Lieberman. Peretz has also demanded the party leader to clarify her political agenda.
During Thursday's speech, Peretz said that as a member of Labor he learned for the first time what it is like to be the subject of "unfounded hatred from within my political party, from my own partners."
"What triggered the wrath?" he pondered. "Was it the fact that I spoke about peace? I really believe that without a peace agreement there won't be social justice. The combination of the two is the key to growth."
Following the primary elections last week, Yachimovich scheduled meeting with all her running mates except for Peretz. Further highlighting the rift between the two, Peretz was absent from an event earlier this week during which the party presented its economic platform.
Earlier Thursday Major-General (Res.) Elazar Stern announced he was joining Livni's party as well.
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