The campaign for the 20th Knesset began with the Likud and Labor looking like they were in cahoots, building each other up by calling it an election between the two largest parties.“It’s us or him,” is the slogan of the Zionist Union that was formed when Labor joined forces with Hatnua head Tzipi Livni in an effort to bring down Prime Minister Benjamin Netanyahu.“It’s us or them,” the Likud responded with its own slogan against Livni and Herzog – always in that order.When the Likud put out an ad featuring the proverbial 3 a.m. phone call from the US president, it showed Herzog and Livni bickering over who should pick it up. Labor responded with its own ad claiming that if Netanyahu wins the election, the president would not even call.When a new Likud ad this weekend portrayed Netanyahu as a “Bibi-sitter” who, unlike Livni and Herzog, can be trusted to protect the nation’s children, the Zionist Union responded with its own ad about why Netanyahu cannot be trusted.Now, the Likud and the Zionist Union have shifted their strategies from building each other up to tearing each other apart. Although they tried, neither list joined with another party in their bloc at the last moment in an effort to win the most mandates and make President Reuven Rivlin’s choice about who should form the government obvious.They are running neck and neck in the polls, and now the only way to ensure that Rivlin will choose one and not the other is to choke the other’s neck. What is the best way to do that? By highlighting the differences between the parties on security, diplomatic, socioeconomic issues or matters of religion and state? Nah. Parties with actual platforms on key issues are the exception, not the rule.Instead the parties are going for the jugular – accusing the other of corruption.The Zionist Union accuses the Likud of various scandals involving the use of public funds by Netanyahu and his wife Sara. The Likud accuses the Zionist Union (without calling it that) of the latest non-profit organization scandal.The effort by both parties to pain the other as corrupt is wise. Before the current Yisrael Beytenu corruption scandal, party leader Avigdor Liberman was seriously talked about as a possible prime minister in a rotation with Herzog.Now that the wounded Yisrael Beytenu has fallen so far in the polls that it is teetering near the threshold, Liberman is consolidating his rightwing base and saying his party would not join a left-wing government.The Likud and the Zionist Union hope to deal the other an equally painful blow. That effort could ostensibly work for one party or the other, or it could bring them both down and help Yesh Atid, which bills itself as the cleanest party.To that end, party leader Yair Lapid has planned an anti-corruption speech for Monday outside Ma’asiyahu Prison, the former home of Shas leader Arye Deri.At least when it comes to corruption, that is an issue the parties are dealing with.