Every government loses popularity in mid-term, especially one lead by a prime minister in his fourth term of office. What is surprising in the two polls published last week in Israel is not that Benjamin Netanyahu's Likud has been overtaken for the first time since the election eighteen months ago, but that the party now leading is not Likud's traditional rival, Labour (or the Zionist Union as it is now branded). It is Yair Lapid's centrist Yesh Atid - and this wasn't supposed to happen.

Israeli politics has a long history of centrist parties which do remarkably well in their first or second election and then evaporate as their leaders squabble over the electoral spoils and disappointed voters gravitate back to the two old beasts, or simply wander on to the next new shiny platform.

Gone are Dash, Tzomet, Shinui (lead by Tommy Lapid, Yair's dad), the Pensioners' Party and Kadima, which was the only centrist party ever to hold power.

All of them initially succeeded beyond expectations and promised to change the political landscape. None lasted more than three Knesset terms.

Yesh Atid seemed to be following the same trajectory.

Mr Herzog has been trying to join the coalition

In 2013, Yesh Atid's first elections, it rocketed to second place with nineteen Knesset seats, propelling Lapid to the key position of Treasury Minister despite zero political experience.

A dismal twenty months in the job ended with his sacking and the coalition's collapse.

Last year, Yesh Atid lost over a third of its votes, though the twelve seats it received was more than expected.

But now, all of sudden, he is riding high again - at least in the polls.

Lapid's rise cannot be ascribed to any major policy he has unveiled or to effectively holding the Netanyahu government to account.

There have been few policies of any substance and Lapid himself has one of the lowest Knesset attendance records.

His current success is largely due to the failure of the official Leader of the Opposition, Labour's Isaac Herzog, to achieve any parliamentary success.

Indeed Mr Herzog has been trying since the election to join the coalition and has been promised the post of Foreign Minister, if he can only get his party to follow him - a hopeless task as his support in the Zionist Union's Knesset faction is about as high as Jeremy Corbyn's in the PLP.

Mr Lapid, on the other hand, has a tailor-made party constitution which ensures his leadership and selection of the Knesset list.

While Labour is rendered ineffective by infighting, Mr Lapid can present Yesh Atid as a government-in-waiting, even if he has yet to specify how they would govern Israel any differently.

None of this means that Mr Lapid has a good chance of becoming Israel's next prime minister. The polls have shown no change in the main political blocs. Yesh Atid's votes are coming from Zionist Union and the center-left bloc remains a minority.

Likud is losing ground to its right-wing partners/rivals Jewish Home and Yisrael Beitenu but Mr Netanyahu is still the undisputed leader of the right-wing-religious bloc, which continues to hold a stable majority.

Elections are not on the horizon but even if Yesh Atid were to become the largest party when they are eventually held, Mr Lapid has no viable path to a coalition.

The Haredi parties will never forget his ultra-secular policies, though he has toned them down of late.

Without their seats, he would have to bridge the unbridgeable differences between left-wing Meretz and Labour and nationalists like Avigdor Lieberman and Naftali Bennett to form a government.

If anything, the latest polls show that if elections were held now, Mr Netanyahu would win once again and Mr Lapid would become the official Leader of the Opposition.