Nazareth, Israel - The legal noose has tightened sharply around the neck of Israeli Prime Minister Benjamin Netanyahu, as dramatic developments on two fronts last week have left him more exposed than ever.

He is due to be questioned by police in two new corruption probes before he leaves for the United States on Thursday. The question is no longer whether Netanyahu will be forced out of office, but how soon, analysts say.

According to reports in Israeli media, senior figures in Netanyahu's Likud party have started calling him "a dead duck".

Netanyahu's biggest setback is a major crack in what observers have termed his "black box" - an inner circle of loyal confidants and aides.

Shlomo Filber, his former bureau chief, agreed to turn state evidence last week, providing the key to unlock a new and more serious corruption allegation: that the prime minister blocked regulation of Israel's telecoms giant, Bezeq, in return for positive coverage of himself and his family from its news website. Police will question him about his role in the coming days.

Netanyahu's downfall 'imminent'

Yaron Ezrahi, a political scientist at the Hebrew University in Jerusalem, said Filber's agreement last Tuesday to give evidence meant Netanyahu's days in office were now numbered.

"He cannot cling on to power much longer," said Ezrahi.

"His downfall is imminent - either he will have to resign or he will be toppled by a rebellion from within his party or the governing coalition.

"His authority has been seriously dented, and the people who have been protecting him are no longer afraid of him," he told Al Jazeera.

The new development comes in the wake of a police recommendation earlier this month to charge Netanyahu with bribery in two other investigations. He is alleged to have helped leading businessmen in exchange for lavish gifts and media support.

Many members of Netanyahu's inner circle are already under severe pressure from police - several have been arrested - as the prime minister's affairs come under close scrutiny in four separate investigations, with a fifth looming.

Separately, Netanyahu's wife, Sara, is facing a fraud indictment over the way she managed the family's official residence.

But Netanyahu can only be charged if Israel's chief law officer, Attorney General Avichai Mandelblit, approves police findings.

It was widely assumed that Mandelblit, who was appointed by Netanyahu, would drag his feet over whether to charge the prime minister.

But Mandelblit is under growing scrutiny, too, after it emerged that the contest for attorney general in 2015 may have been conditioned on the winner dropping what was then a preliminary investigation into Sara Netanyahu.

Ezrahi said Mandelblit would find it much harder to draw out the proceedings in the current circumstances. "His options to delay bringing charges are pretty much exhausted," he said.

Filber, Netanyahu's former bureau chief, is reportedly the key witness needed by police, seeking to confirm allegations that Netanyahu helped Bezeq in return for favours from its controlling shareholder, Shaul Elovitch.

The suspicion is that Netanyahu parachuted Filber into the top post in the communications ministry to stymie competition reforms that would have severely damaged Bezeq's commercial position.

In exchange, police believe Elovitch offered to provide the prime minister with favourable coverage from Walla, a major online news website he also owned.

Other investigations

The investigation - dubbed Case 4000 - has echoes of another investigation, Case 2000, over which police have already recommended Netanyahu be charged with bribery.

In that case, Netanyahu was taped apparently cutting a deal with Arnon Mozes, owner of Israel's influential Yedioth Ahronoth news group. The Israeli prime minister is heard suggesting legislation to weaken a rival newspaper, Israel Hayom, in return for positive coverage from Yedioth to help him stay in power.

Police have also recommended Netanyahu be charged in Case 1000, in which he is suspected of receiving nearly $300,000 in gifts from businessmen, in return for lessening their tax bills and providing them with investment opportunities.

A fourth investigation, Case 3000, has so far implicated a large number of Netanyahu's aides and former advisers, though not yet directly the prime minister. They are suspected of receiving bribes from a $2bn deal with a German manufacturer of Dolphin submarines, which are capable of carrying nuclear warheads.

Ezrahi said there were strong suspicions that Netanyahu could not have been ignorant of such kickbacks, given the national security implications of the subs' purchase. He is expected to be questioned about his role in the affair this week.

Ben Caspit, who has been at the forefront of reporting developments in the various investigations, observed last week that Filber's cooperation with the police on Netanyahu's telecom investigation could "open a bottomless Pandora's box".

A theme emerging from the investigations is Netanyahu's apparently increasingly desperate efforts to rig the Israeli media in his favour, to maintain his grip on power.

Yossi Alpher, who served as an adviser to Ehud Barak, a former Israeli prime minister, noted after the 2015 general election Netanyahu reserved the post of communications minister for himself. As part of a coalition pact, he insisted his coalition partners approve any decisions he made in that capacity.

"It looks very much like he was seeking near-complete control over the Israeli media and his public image," Alpher told Al Jazeera.

As well as allegedly making secret deals with the businessmen behind leading newspapers and websites, Netanyahu threatened punitive moves against Israel's two largest commercial broadcasters, Channels 2 and 10.

He also sought to move control of the popular Army Radio to the defence ministry, making it easier for the government to interfere in its coverage.

Senior journalists coming forward to tell of how they were leaned on to provide uncritical coverage of the Netanyahus have strengthened suspicions of meddling.

Last week, it was reported that Ilan Yeshua, chief executive officer of the Walla news website, had handed over to police recordings of Elovitch, Bezeq's majority shareholder, demanding he slant coverage to help Netanyahu.

In an indication of how entangled the various investigations are becoming, Netanyahu reportedly wanted Walla's chief editor, Aviram Elad, sacked for publishing a report into improprieties in another investigation - the purchase of the Dolphin subs.

According to Alpher, the cases piling up are an indication of the extent of Netanyahu's "megalomania.

"What they highlight is a catastrophic combination of ego, instinct for survival and political paranoia," said Alpher.

'Victim of police persecution'

So far, Netanyahu has held on to power because his core supporters have been unmoved by the mounting evidence against him.

A poll after last week's revelations showed his party would still win the biggest share of seats if parliamentary elections were called.

Netanyahu has claimed he is the victim of police persecution.

Last week, Likud legislators unsuccessfully tried to mount a full-frontal attack on the right-wing police commander Roni Alsheikh at an interior committee hearing. The legislators accused Alsheikh's force of carrying out a politically motivated "coup" against the prime minister.

According to Haaretz analyst Amos Harel, the public assault on Alsheikh was intended as a warning to Mandelblit, the attorney general, of what lay in store for him if he moved to charge Netanyahu.

But the attorney general is now under greater pressure to act decisively, after he found himself implicated in a potential new scandal.

It emerged last week that, in 2015, Hila Gerstl, a former judge, was approached by Nir Hefetz, Netanyahu's former media adviser, offering her the post of attorney general if she promised to close legal proceedings against Sara Netanyahu.

That has left a dark cloud over Mandelblit, a former cabinet secretary for Netanyahu, who got the job instead. It raises concerns about how much Netanyahu interfered in the appointment and whether Mandelblit was offered - and agreed to - a similar deal.

The Israeli media has questioned whether Mandelblit himself should be investigated and whether, as a result, he should recuse himself from the other Netanyahu investigations.

In a statement last week, Netanyahu dismissed the report about Hefetz, saying his adviser "never made such a ludicrous offer".

'Crimes against humanity'

Alpher, the former adviser to Ehud Barak, said Netanyahu had no choice but present a public image of "business as usual", but that, behind the scenes, his options were narrowing.

He could resign, as his predecessor Ehud Olmert did, to concentrate on his defence; seek a plea deal in the hope he would avoid prison time in return for his resignation; or call new elections while he still has popular support.

"The last option would be risky. It would probably make no difference to his fate, if the legal case is as solid as it looks. And there is the chance it would spur more revelations."

Jamal Zahalka, a Palestinian member of the Knesset for the Joint List, said Netanyahu's indictment for financial irregularities should be compared to the American gangster Al Capone's conviction for tax evasion in the early 1930s.

"Netanyahu has committed crimes against humanity and is responsible during his premiership for the deaths of innumerable Palestinians," he told Al Jazeera.

"He should be tried for those crimes, not for his appetite for expensive cigars and champagne."