Some 50,000 registered members of the Labor party, which heads the opposition, choose their next leader Tuesday from among the largest number ever of contenders. The five realistic hopefuls are the incumbent secretar general Yitzhak Herzog, three new faces – Avi Gabay, Omer Barlev and Erel Margalith – and one veteran, Amir Peretz. If none scores 40 percent, the voting goes to a second round in a week’s time. Labor after amalgamating with Tzipi Livni’s party won 24 of the 120 Knesset seats in the last general election two years ago. But since then, it is in a downward spiral in the opinion polls.