He insisted, plausibly, that the national camp as a whole could be forced out of power if the Zionist Union, not the Likud, won a plurality of seats and was granted the mandate, by President Reuven Rivlin, to try to form a majority government.
The hard right sees the union of Labor and Likud as glorious confirmation that Israelis are finally sobering up and discarding their illusions about peace.
For months, Herzog and Livni's Zionist Union and Netanyahu's Likud had traded a one-seat edge in the polls, but over the past week the opposition had opened a three-to-four-seat lead.
Even a grand coalition of the rivals Likud and Zionist Union, the two largest factions, would be unable to secure a majority.
Given that gap between Likud and Zioonist Union it is hard to imagine him defecting to Zionist Union.Even if he were to do so, Mr Herzog would still find it nearly impossible to form a majority.
And if the election turns out as close as the polls currently suggest, President Reuven Rivlin could insist on negotiations for a national unity government embracing both Likud and Zionist Union.
The latest polls show Netanyahu's Likud and the Zionist Union neck and neck.
A second poll published jointly by the Jerusalem Post and Maariv dailies showed the same four-seat gap between the parties, with the Zionist Union winning 25 against 21 for Likud.
Likud and [the Zionist Union's] Tzipi Livni and Isaac Herzog are close.
The win comes as a surprise, as Likud trailed the Zionist Union in the latter stages of the campaign.
And as the count came in he pulled ahead to score a clear victory, of 30 seats for Likud to 24 for Zionist Union, that will secure him a fourth term.
