By Gabriel Partos BBC south-east Europe analyst

Montenegro's second attempt within two months to elect a president failed on Sunday when the turnout in the nationwide vote failed to reach the required 50%.

For many people disappointment with politics is turning into electoral apathy

The same thing has already happened in neighbouring Serbia - Montenegro's bigger partner in what was, until last week, Yugoslavia.

The speaker of the Montenegrin parliament, Filip Vujanovic, will now carry on as acting president - just like his opposite number in Serbia, Natasa Micic - until a head of state is elected.

But what is behind the failure in each of these cases to elect a president and who, if anybody, is benefiting from it?

Mr Vujanovic, the candidate of Montenegro's pro-independence governing coalition, won an overwhelming majority of the votes - more than 80% - in Sunday's presidential election, just as he had done during his first attempt seven weeks earlier.

But once again he failed to get elected because, according to unofficial figures, the turnout was around three percentage points below the required 50% of the electorate.

Vujanovic seems likely to be elected Montenegrin president

There were several reasons for the low turnout. Voter fatigue was one - this was, after all, the fourth nationwide ballot to be held in Montenegro within nine months following municipal and parliamentary elections and the first round of the presidential poll.

Heavy snow meant that around one in 14 of polling stations could not open.

But the most important factor behind the failure of the ballot was the decision of the main anti-independence opposition bloc - known as Together for Change - not to have its own candidate. Most of its supporters boycotted the polls.

Kostunica failure

The situation is not unlike that in Serbia - Montenegro's partner in what was until last week federal Yugoslavia and has now become the much more loosely-knit union of Serbia and Montenegro.

There, too, outgoing Yugoslav President Vojislav Kostunica came first on three occasions during the Serbian presidential race last autumn. But he, too, failed to pass the required electoral hurdles.

And on the last occasion, in December, that was mainly because his main political rival, Serbian Prime Minister Zoran Djindjic, held back from running his own candidate.

For Mr Kostunica the repeated failure to get elected was a slap in the face - both from Prime Minister Djindjic and from the Serbian electorate.

He had enjoyed overwhelming popularity after he defeated the authoritarian post-communist leader, Slobodan Milosevic, in the Yugoslav presidential elections nearly two and a half years ago.

He is still soldiering on in a caretaker capacity as the president of the now defunct Yugoslavia - before the parliament of the newly formed union of Serbia and Montenegro convenes to select a head of state.

Once Mr Kostunica steps down, he will lose his power base within the federal institutions, including sections of the army high command.

Constitution rethink

He will have no important office in any of the institutions of the state.

Kostunica's failure is a slap in the face

That suits Prime Minister Djindjic, who believes this will weaken Mr Kostunica and his party.

For that reason, Mr Djindjic is keen to postpone any further attempts at electing a Serbian president until the republic's constitution has been changed to take into account the departure of Mr Milosevic's authoritarian regime and the end of the Yugoslav federation.

A new constitution will take at least six months - and possibly much longer - to draft.

In the meantime, Mr Djindjic is happy to have a political ally, such as Ms Micic, continuing the fill the role of acting president.

The longer the vacuum at the presidency, the longer presidential and parliamentary elections are postponed, the more Mr Djindjic believes he can consolidate his own position.

Union presidency

By contrast, Montenegro's Prime Minister Milo Djukanovic is in more of a hurry.

This was Montenegro's fourth nationwide ballot in nine months

Although his acting president, Mr Vujanovic, is a reliable ally, it would make more sense for Mr Djukanovic to see Montenegro's political stability strengthened by having an elected head of state.

It now looks likely that Montenegro's election law will be amended to abolish the turnout requirement.

That will make it possible for a fresh presidential election to be held in the next two to three months. Judging by the latest results, Mr Vujanovic will then, all likelihood, be elected president.

However, the first of the presidential vacancies to be filled is almost certain to be at the head of the union of Serbia and Montenegro.

It is expected that the newly-formed union's parliament will meet later this month, and MPs will then pick one of Mr Djukanovic's colleagues, Svetozar Marovic as president.

The choice of the new Serbian-Montenegrin union's president will be based on political wheeling and dealing. Many Serbians and Montenegrins feel disillusioned with the way politicians operate - perhaps more so in Serbia where the fall of Mr Milosevic raised expectations of a different kind of fresh start.

Now, for many people disappointment with politics is turning into electoral apathy.