Yesterday marked a critical juncture in Israel’s campaign season. That turning point came in the form of a surplus vote agreement, quietly negotiated between Avigdor Liberman’s Yisrael Beiteinu and Benny Gantz’s Kachol Lavan. It could seal Prime Minister Benjamin Netanyahu’s political fate, but it also carries serious risks for Liberman and his potential partners in Kachol Lavan.

Seats in Israel’s Knesset are assigned according to the portion of the national vote a given party receives. However, a party cannot receive half a seat. A surplus vote (or vote sharing) agreement dovetails this problem, stipulating that votes that would not equal a full Knesset mandate are apportioned to the party with a greater number of excess votes. It is not a joint list or unified campaign, but it does signal common interests and a willingness to work together.

Liberman is presenting the move as a purely technical measure. Most Israeli political parties routinely enter into surplus vote agreements, although Kachol Lavan was notably left out of any such arrangement in April. But the parties that reach these accords would typically sit together in a coalition, while Avigdor Liberman had publicly vowed not to recommend Benny Gantz as prime minister in the leadup to April’s election and during coalition negotiations (promises the Yisrael Beiteinu chief made good on). Thus, the new surplus vote agreement is a big deal because it marks the first instance of practical cooperation between Yisrael Beiteinu and Kachol Lavan.

News of the surplus vote agreement coincided with a report suggesting that members of Yair Lapid’s centrist Yesh Atid faction had mulled splitting off from Kachol Lavan to run a joint ticket with Yisrael Beiteinu. Lapid supposedly blocked any such proposal, citing his commitments to his Kachol Lavan running mates. The idea may have piqued Liberman’s curiosity, although both parties denied the affair in public.

The emerging relationship between Kachol Lavan and Yisrael Beiteinu throws the ball into Benjamin Netanyahu’s court. Avigdor Liberman has been consistent throughout the campaign in calling for a national unity government including his own party along with Likud and Kachol Lavan. However, up until now Liberman’s commitments were verbal only, with no concrete steps demonstrating he would follow through following elections. While a surplus vote agreement does not bind Liberman to anything after election day, it is certainly a major step toward a future partnership. All indications are that Likud cannot form a coalition without Yisrael Beiteinu. If Liberman is firmly committed to working alongside Kachol Lavan, and Kachol Lavan remains unwilling to sit with a prime minister facing indictment, then Benjamin Netanyahu will be in serious trouble after September 17.

Yet even with mounting pressure against the prime minister, there are still a couple of ways this latest development could backfire against Liberman and Kachol Lavan.

First, partnering with Liberman narrows Kachol Lavan’s list of potential partners. While the Yisrael Beiteinu head has taken great care over the past few months to refashion himself as a moderate in the eyes of the Israeli public, some segments of the electorate understandably still see him as a right-wing radical. Nothing in a surplus vote agreement obligates Kachol Lavan to sit with Liberman in a government, but the mere affiliation may be sufficient to turn off others to Gantz’s list. Just last week, Ehud Barak stated that the Democratic Union would not join a government with Liberman. For his part, Liberman has stated that he wants to exclude Meretz (now part of the Democratic Union) and Labor, both parties that might have otherwise linked up with Kachol Lavan in a coalition. This means that if Gantz and his partners continue courting Liberman, a unity government will go from being Kachol Lavan’s preferred option to being its only option.

If Liberman is too right-wing for some on the center-left, Kachol Lavan may be too left-leaning for Liberman’s base. Netanyahu has been working tirelessly (and largely unsuccessfully) to peel votes away from Yisrael Beiteinu’s base of older Russian-speaking immigrants. Among other things, the prime minister has charged that Avigdor Liberman is a leftist, an accusation that lacked any weight given Liberman’s right-wing nationalist record. Kachol Lavan is hardly left-wing, but it is easier for the prime minister to paint his centrist challengers as such. Liberman’s formal relationship with Kachol Lavan could make the prime minister’s attacks look slightly more credible. Yisrael Beiteinu sharply denounced the recent rumors that Yesh Atid members had sought to run with Liberman on a united list, describing the report as the product of a “sick imagination.” Liberman is clearly aware of how associations to his left may look to voters, further stating in a radio interview that he accepts the risks connected to a surplus vote agreement with Kachol Lavan. However, it’s too early to tell what the impact of that agreement among Yisrael Beiteinu’s base will be.

Vote sharing is fairly routine in Israeli politics, but the growing ties between Yisrael Beiteinu and Kachol Lavan are anything but mundane. Whether it sinks Netanyahu or splits the opposition, this relationship is one that will carry ramifications well past election day.