Compulsory military service for yeshiva students is a popular issue for secular politicians. But Shas and other Orthodox parties will continue to get their way on this issue, partly because of Israel's fragmented electoral system, but also largely because Zionism depends on the haredim for its raison d'être. By Steven A. Cook Washington -- Last week the Israeli media reported that Shas spiritual leader, Rabbi Ovadia Yosef, suffered a minor stroke. Although his doctors were mum on what might have caused the episode, sources close to Yosef indicated that a contributing factor was the rabbi’s fear of a renewed push among…