Mr. Gantz’s endorsement of the plan, at least as a basis for negotiations, made it less partisan but also blurred the lines between his party and Likud. Mr. Netanyahu has mockingly referred to Mr. Gantz as a “Bibi from AliExpress,” using his own nickname to denigrate his rival as a cheap imitation of himself.

To remain in power, Mr. Netanyahu needs Likud to be the largest party and for the right wing-religious bloc to beat the center-left bloc. In the last two elections, however, the pro-settlement parties squandered votes because of internal squabbling and political fragmentation, a result that could easily repeat itself on Monday.

In September, more than 58 percent of Yitzhar’s voters cast their ballots for Jewish Strength, a tiny extreme right-wing party that advocates Jewish sovereignty over the entire West Bank and other occupied territories and the transfer of “enemies of Israel,” meaning Palestinians, to neighboring Arab countries.

But the party failed to win enough support to enter Parliament, and the more than 80,000 votes it garnered went to waste. The party has insisted on running again, despite Mr. Netanyahu’s pleas for it to drop out of the race and channel its voters to him or allied right-wing parties large enough to be assured of representation.

Yitzhar, southwest of the Palestinian city of Nablus, is home to the Od Yosef Chai seminary, whose students have a reputation for violence against Palestinian villages and for clashing with Israeli security forces who try to curtail their activities. Some Yitzhar voters are now deliberating between the pro-settlement Yamina party and the ultra-Orthodox United Torah Judaism.

“In the big picture Netanyahu did great things,” said Yechiel Klein, 37, another member of Yitzhar’s council. “But we’d like to see a stronger stand on the things we believe in.”