Sometimes the world can change radically, practically turning upside down, in only a few moments.

Only such a radical change could explain Bat Yam Mayor Shlomo Lahiani’s sudden, shocking decision on Thursday to willingly cut a plea bargain with the state that will almost certainly end his political career and may land him in jail for a year.

What was the change? In July 2012, former prime minister Ehud Olmert was mostly acquitted in his Jerusalem corruption trial and commentators spoke of an “Olmert effect” in which many public officials became more brazen and confident that they could beat the prosecution’s public corruption charges in court.

A notable result was Attorney- General Yehuda Weinstein’s explicit mentioning of having considered the “impact” of the Olmert ruling when he decided in December 2012 to close a decade-long investigation against Foreign Minister Avigdor Liberman for millions of dollars in alleged money-laundering.

In place of that juggernaut of a case and despite a decade of investigations, Weinstein moved from having favored an indictment in 2011 to closing the case without firing a shot a few months after Olmert’s acquittal.

In place of that “big case” against Liberman, a much smaller indictment was filed.

With Liberman’s acquittal in that case in November 2013, commentators talked of the prosecution’s deterrent powers being eroded to an alltime low.

All of that changed in one moment when Olmert, former Jerusalem mayor Uri Lupolianski, former Bank Hapoalim chairman Dan Dankner and seven other prominent figures were all convicted of bribery on March 23 in the Holyland real-estate corruption trial.

The bruised and broken prosecution got back its swagger and then some.

The conversation shifted from whether the state could get big convictions anymore to whether Olmert and company would serve 1-2 years of prison time on average or as many as 6-8 years.

Suddenly the “Olmert effect” represents not the state’s weakness, but its intimidatingly strong record in bringing down the highest officials, including getting them jail time.

Back to Lahiani. Lahiani has been fighting bribery and corruption charges for years now and has proclaimed he would fight to the end over and over again.

The impression was he not only believed he could get off on the charges, but that he was so confident, that he was more concerned about ensuring the case did not affect his soaring political ascent as one of the country’s most popular mayors than he was about the case itself.

If Lahiani was planning all along to cut a plea bargain, which very likely will make him ineligible for public office for seven years and may send him to jail for 12 months, why not save himself tons of legal fees and negative media attention by cutting the deal months or years ago.

Why cut a deal at such a late date, but within the trial itself, nearly right after it started? The answer appears to be clear.

He had been ready to fight until the end. Then the world changed.

The Olmert effect was redefined and he started to think that his biggest concern should not be staying in politics, but staying out of jail.

The deal with the state drops the bribery charges that Olmert and company were convicted of.

Whereas Olmert’s worst-case scenario could include six years in prison, Lahiani’s worst case will now be one year.

His political career is likely over, but even if you’re an ex-politician there are many better things to do with your time than spend it in jail.

There are three other mayors under the gun on corruption charges. If more of them start to fall and cut deals, then the Olmert effect will truly have empowered the state with an unprecedented level of deterrent power.

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