A new odd couple in Israeli politics has become the biggest obstacle to Prime Minister Benjamin Netanyahu's effort to form the next government.

The surprise alliance between Yair Lapid, 49, the rising star of Tel Aviv's secular elite, and Naftali Bennett, 40, the yarmulke-wearing head of a religious-nationalist party, has added an unexpected wrinkle to coalition talks.

Nearly a month after the election, Netanyahu has yet to announce a single partner, with a mid-March deadline looming.

That's largely because Lapid's center-left Yesh Atid, the Knesset's second-largest party with 19 seats, and Bennett's far-right Jewish Home, which has 12 seats, have set aside ideological differences on the Palestinian conflict and told Netanyahu that each will join the government only if the other does as well. Lapid puts a two-state solution near the top of his agenda, while Bennett bitterly opposes Palestinian statehood.

Because it may be impossible for Netanyahu to secure a majority in the parliament without at least one of those parties, the pact is making it harder for Netanyahu to play them against each other. It may also force him to make some difficult political decisions in the coming weeks about whether to draft ultra-Orthodox students into the army and how to restart Palestinian peace talks.

It's not the first time political rivals and ideological foes have joined forces in Israel's coalition government system. Historically such alliances don't last. But so far the partnership appears to be holding.

"There is a considerable common denominator between us on many things," Bennett said recently during a speech to American Jewish group leaders, noting they both support a military draft for the ultra-Orthodox.

By focusing on the areas of agreement, Bennett said, the alliance offers a "rare opportunity" to tackle political hot potatoes. "I can't say we agree on everything, but I think it's good news that we have so much common ground," he said.

Netanyahu's negotiators are trying hard to bust up the pact.

"Netanyahu is working to divide and conquer by trying to identify the weak link, the soft spot for cutting a deal," said Ofer Kenig, a political analyst for the Israel Democracy Institute.

Conservatives are focusing pressure on Bennett, accusing the former high-tech entrepreneur of betraying his beliefs and supporters. Likud member and Vice Prime Minister Moshe Yaalon told Israel's "Meet the Press" program Saturday that the pact was a "deception" and "slap in the face" of Jewish Home voters.

At the same time, in an attempt to sweeten the deal, Netanyahu reportedly offered Bennett the post of education minister and promised senior government jobs to other Jewish Home lawmakers if the party would drop its alliance with Yesh Atid.

Though some predict Bennett may ultimately be forced by his conservative supporters to accept Netanyahu's offer, so far he has said it is too early to discuss jobs until the structure and philosophy of the coalition are clear.

Lapid's party has also reportedly been offered its pick of government positions, but the former TV broadcaster told the prime minister that he would join a government only if it is committed to drafting religious students, restarting Palestinian peace talks and limiting the size of the next Cabinet.

Netanyahu is now exploring whether he can reach a Knesset majority without either Yesh Atid or Jewish Home.

He has met at least twice with one of his biggest critics, Labor Party Chairwoman Shelly Yachimovich, offering her the plum position of finance minster if she would bring her party's 15 seats to the coalition, according to Israeli press reports. Yachimovich dismissed the reports and said she would not join Netanyahu's government.

If Netanyahu is unable to find 61 seats in the 120-member Knesset, he may accept the demands of Lapid and Bennett to draft religious students into the army for the first time.

That would probably create a split between Netanyahu and the ultra-Orthodox parties Shas and United Torah Judaism, which were reliable partners in Netanyahu's last government.

Without the support of the religious parties, which together have 18 seats, Netanyahu would be far more dependent upon Lapid and Bennett for his government's survival. His supporters see that as a political trap.

Shas leader Eli Yishai said Sunday that Lapid and Bennett were trying to sideline the ultra-Orthodox and he called their alliance "a roadside bomb that will explode at some point in an attempt to bring down the prime minister."

Yesh Atid members say their goal is secure clear commitments from Netanyahu to ensure that a religious draft and other priorities don't fall victim to political horse-trading or delay tactics.

"We are not asking for another committee to explore the issues," said Yesh Atid lawmaker Dov Lipman. "We want a written coalitional agreement that says we will legislate our platform."

It remains to be seen whether the Lapid-Bennett alliance can endure, particularly when navigating the Palestinian issue. So far, much of the strategy appears to be based on personal chemistry between two rising political stars and Knesset newcomers.

"It's something very personal," said Hebrew University professor Gideon Rahat. "Both men are relatively young, successful and rich. But looking further down both [Knesset] lists, it is hard to see any common denominators among the other members.... Ultimately parties and ideologies will prevail when they get down to business."