The formation of Likud Beiteinu - this past weekend's political bombshell - requires all of Israel's political players to regroup and make some clear and binding statements to their voters, right now.

It's not enough to express shock and anger. The center-left bloc, and even some people in the Likud who are terrified at what awaits Israeli democracy as a result of making Avigdor Lieberman such a central force in the party, have no choice but to respond unequivocally. It is time to act.

Labor party chairwoman Shelly Yacimovich must immediately announce that she will not, under any circumstances, join a coalition formed by Likud Beiteinu. If she does not do so, let all voters be warned that a vote for Labor is a vote for a Likud Beiteinu government.

Yacimovich cannot continue to blur her positions and hide behind shallow slogans like her statement, "Joining Netanyahu is an imaginary development," as she did over the weekend. Israel's political reality often reaches beyond one's wildest imagination, and thus she must make it clear where she's heading and what her red lines are. Being part of a Netanyahu-Lieberman government must be out of the question for someone who seeks to lead Israel's leftist camp.

Yesh Atid chairman Yair Lapid must also clarify his stance. The voter deserves to know whether or not the new hope of the center will or will not join an extreme rightist government. Similarly, the other personalities who make up the center of the political map - Ehud Olmert, Tzipi Livni, Shaul Mofaz and others, even if they haven't decided to run - must tell the voters whether they intend to join a right-wing government.

A special responsibility lies on the shoulders of several major Likud figures, members of the party's more moderate wing, most of whom have been holding their peace. Michael Eitan, Reuven Rivlin, Dan Meridor, Benny Begin and a few others who proclaim the supreme value of democracy must launch a fierce battle within their party against this dangerous move, and not wrap themselves in silence.

Grumbling isn't enough now. This is a test for those who are not part of Israel's extreme right. This a moment of truth for Israeli politics.