In a dramatic reversal, Israeli Prime Minister Benjamin Netanyahu's chief rival, Benny Gantz, has agreed to join forces in an "emergency government" to deal with the coronavirus crisis.Why it matters: This is a big step toward ending Israel's year-long political deadlock and a victory for Netanyahu, who will stay on as prime minister for at least another 18 months even as his corruption trial gets underway.According to the draft deal with Netanyahu, Gantz will serve as vice prime minister and then become prime minister after 18 months. Gantz's advisers say they will have the agreement enshrined in law, though it's unclear whether that will be possible. Many of Netanyahu's critics argue he can't be trusted to leave office as promised.Gantz's faction will also control the Defense, Foreign and Justice ministries, among other roles.The backstory: Gantz and his Blue and White party ran in three consecutive election campaigns, all in the last year, on a platform of replacing Netanyahu at all costs. Gantz repeatedly said he would not be serving under Netanyahu while the prime minister was under indictment.He had even promised to pass laws to prevent a prime minister from taking office after being indicted. Today's move will enrage members of his political base, the vast majority of whom are vehemently opposed to Netanyahu.The move is particularly extraordinary because it comes just over a week after Gantz received a presidential mandate to form Israel's next government.Gantz had said he intended to form a unity government to deal with the coronavirus crisis, but with him as prime minister.Netanyahu, meanwhile, has called on Gantz almost daily to join an emergency unity government.Behind the scenes: Gantz and his advisers held secret talks with Netanyahu and his aides for several weeks — elements of which were not disclosed even to Gantz's political partners in the Blue and White leadership.Meanwhile, Gantz's opposition bloc started to use its majority in the Knesset, Israel's parliament, to take control of key committees.Blue and White even pushed for a vote to remove a Netanyahu ally as parliamentary speaker, leading to an unprecedented constitutional showdown involving the supreme court.The political drama reached its climax today, ahead of a planned vote for the next speaker. Netanyahu threatened to rule out a unity government if Blue and White's original nominee — who came from another party faction led by Yair Lapid — was selected.Two hours before the vote, Gantz told Lapid he would not support the nominee and would propose himself to be speaker instead in order to buy more time for negotiations with Netanyahu.Lapid told Gantz that would be the end of Blue and White, but Gantz still went ahead.Lapid and another leader within the party, Moshe Ya'alon, announced they would be splitting the party. That move gives them 18 seats in the Knesset to Gantz's 15.