Prime Minister Benjamin Netanyahu bolstered his status as the “Mr. Surprise” of Israeli politics on Thursday afternoon.

Five months after he shocked the political establishment by concluding an alliance with the centrist Kadima Party to stave off elections — a partnership that collapsed less than three months later — he and Foreign Minister Avigdor Liberman secretly hatched an alliance that will see their respective Likud and Yisrael Beytenu parties run together on a joint list in the elections, which were recently set for January 22.

But while Kadima’s Shaul Mofaz was emphatically a minor, privately derided player in that earlier brief alliance, Liberman, smiling and at ease in his joint press conference with Netanyahu on Thursday night, is now clearly the prime minister’s right-hand man and would-be heir apparent. At 54, Liberman is nine years Netanyahu’s junior; Thursday’s alliance, should it prove viable, paves the way for him to seek the top job, sooner or later.

A key motivation for their partnership may have been concern that former prime minister Ehud Olmert could return to politics — having resigned four years ago amid corruption allegations — and that a center-left party including Olmert, his former foreign minister Tzipi Livni, and others, might — however improbably — win more seats than the Likud come election day.

But the deeper context is that Netanyahu and Liberman, a 1978 immigrant from Moldova who lives in the settlement of Nokdim, have long been political allies, and that this partnership has been much discussed between them in the past few years. Liberman served as the director-general of Netanyahu’s office when the Likud leader was first prime minister in the late 1990s. Liberman then split away to form Yisrael Beytenu, a party with particular appeal to voters — like himself — from the former Soviet Union. But although he has charted a political course a little to the right of Netanyahu’s Likud in recent years, and although there have been suspicions and political disagreements between the two men — notably over Palestinian Authority President Mahmoud Abbas, whom Liberman regards as a “political terrorist” but with whom Netanyahu says he would negotiate — they have become increasingly close in recent years.

The next few weeks will determine whether their parties are more attractive together than separately. Their aides claimed Thursday afternoon that internal polls indicate that the 42 seats they hold jointly at present — 27 for the Likud and 15 for Yisrael Beytenu — will swell to more than 50, out of the 120 in the Knesset, when they run together. But the arithmetic is not immediately persuasive. Twenty-seven plus 15 does not ordinarily add up to 50.

It is hard to identify the tens, even hundreds of thousands of new voters who those polls purportedly prove will be drawn to this alliance, and easier to envisage moderate Likudniks feeling they don’t quite belong under the expanded “Biberman” roof.

One thinks of that proportion, albeit small, of the Likud camp that sees itself as following dovish Likud “prince” Dan Meridor, for instance. What, one wonders, was Meridor thinking when the news broke?

Then there is the rather larger group of Orthodox Likud voters, for whom Liberman’s secular constituency and outlook — and his consequent pressure for ultra-Orthodox conscription and eased conversion processes — are anathema.

In party political terms, Netanyahu’s new marriage to Liberman would seem to signify divorce from Shas. And Shas has just celebrated the return of Aryeh Deri, who is certainly no hawk when it comes to the settlements and who might just, depending on the election results, want to whisper something into Rabbi Ovadia Yosef’s nonagenarian ear about Netanyahu’s betrayal of his loyal ultra-Orthodox coalition partners.

Leaders of the center-left opposition, having recovered from the shock of the news, unsurprisingly asserted that the gambit would backfire on Netanyahu, and whispered that the prime minister had panicked because the Likud’s poll numbers aren’t high enough. The merged parties would be “a North Pole of extremism,” claimed Labor’s Isaac Herzog. Those more moderate Likud voters, alarmed by the alliance with the hawkish Liberman, would abandon the new pairing, Herzog predicted, and plump for Labor.

Aides to Netanyahu were hinting that the prime minister has more political surprises up his sleeve. One issue, however, is whether an unpleasant surprise is awaiting Liberman. He has been the subject of an extremely long-lasting corruption allegation, which the attorney general’s office has reportedly promised to resolve — either by indicting him, or closing the case — before the elections.

Another potential obstacle to a soaring new alliance is the response of other would-be Likud prime ministers; the likes of Silvan Shalom and Moshe Ya’alon, self-regarded leaders-in-waiting, did not rush to laud the unexpected partnership on Thursday afternoon.

The announced joint list is also likely to add momentum for calls for a similar alliance on the center-left — perhaps bringing Labor, resurgent under Shelly Yachimovich, into some kind of partnership with the faltering Kadima, and with the new rising star of Israeli politics, Yesh Atid leader and ex-TV anchor Yair Lapid. Were these various players to put aside their differences, they might create some political momentum of their own, exposing a gamble Netanyahu did not have to take as one he should have avoided.

Reports Thursday night indicated that their deal allows Liberman to choose any post he wants in Netanyahu’s coalition. But Liberman’s eye has long been fixed on the top job, and he has always known that he could not become prime minister as head of a relatively minor faction like Yisrael Beytenu.

The route to the prime ministership for Liberman required a return to the Likud, where he served as director-general of the party under opposition leader Netanyahu in the early 1990s.

Now Netanyahu has opened a potential path for his longtime aide, ally and occasional rival to seek, sooner or later, to succeed him. Right now, as that short-lived alliance with Kadima underlined, it is still Netanyahu who holds most of the cards. Time will tell whether he will come to regret giving some of them to Avigdor Liberman.