It's doubtful the media ever assessed David Ben-Gurion's "first 100 days"; or Moshe Sharett's - or, for that matter, Menachem Begin's. The idea of evaluating the first 100 days of a modern head of government originated with the American presidency of Franklin Delano Roosevelt, who came to power in 1933 at the height of the Great Depression. Said political scientist Robert DiClerico: "The first hundred days of his administration were a bustle of activity, producing the greatest waterfall of legislation of any president in [US] history." Most of FDR's successors found him a hard act to follow. But the 100-day milestone stuck and eventually gained momentum even outside America. In Britain, for instance, Margaret Thatcher's leadership was critiqued in June 1975, 100 days after she assumed office - and that's been the case with every premier down to Gordon Brown. Nicolas Sarkozy, among other European leaders, came into office promising results "within 100 days." BINYAMIN Netanyahu may have imported the "first 100 days" concept to this country when he became premier in 1996 and pledged to come up with a list of state-owned companies that would be privatized. He didn't. Ehud Barak's first 100 days were charitably evaluated, in October 1999, as "at least setting the stage" for fulfilling the promises he had made in his campaign. When Ariel Sharon was elected to pick up the pieces of Barak's premiership, his first 100 days were devoted to figuring out how to defeat Yasser Arafat's second intifada. Yet Sharon still managed to obtain Knesset support for a bold economic recovery plan. Prime Minister Ehud Olmert's first 100 days were upstaged by the kidnapping of Gilad Schalit and the collapse of his convergence plan. Now the first-100-day criterion has come back to haunt Netanyahu, with Kadima opposition leader Tzipi Livni attacking his government for zigzagging, lack of direction, and failing to address the economic crisis. Her party unveiled a bumper-sticker - "Bibi's the same Bibi. 100 days, zero accomplishments" - which reportedly upset the premier when an aide showed it to him. Meanwhile, on the steadfast Right, Netanyahu is being pilloried for turning his back on what was understood to be his pledge to oppose a Palestinian state. NO ONE can fault the premier when unprincipled reporters ambush his venerable 100-year-old father to extract assertions that make the son look like a dissembler. Yet the criticism that Netanyahu has been zigzagging, on both foreign policy and domestic issues, is not without merit. He hesitated too long before making his Bar-Ilan speech articulating mainstream Israel's acquiescence in a demilitarized Palestinian state. He misguidedly enlarged Defense Minister (and embattled Labor Party chief) Ehud Barak's portfolio to make him de facto special envoy to the Obama administration. By sidelining Foreign Minister Avigdor Lieberman, Netanyahu has been signaling a "soft" negotiating strategy when, arguably, a better bargaining approach - given President Obama's apparently resolute determination to force a categorical and unconditional settlement freeze on Israel - would have been to let the pragmatic but tough Lieberman play his scripted role. The government has also been ineptly leaking its compromise proposal for a settlement freeze before locking in Washington's assent, eliciting State Department denials and making a face-saving compromise harder to achieve. In the domestic sphere, Netanyahu's first 100-day flip-flops on budget cuts and, this week, on the proposed imposition of VAT on fruits and vegetable, have manifestly undermined his credibility. On the positive side, he's advocated a two-year budget process, which if implemented will promote fiscal stability. He has sought to codify the Bank of Israel's independence. His championing of a bill to reform the Israel Lands Administration, while problematic, deserves to be frankly debated. AT THE end of the day, Israel's hyper-pluralist political system cannot fairly be compared to America's, or even Britain's forms of government. For an American president, the 100-day countdown is typically accompanied by a political honeymoon. Not so in Israel, where Netanyahu was forced to cobble together a coalition of ideologically disparate parties, making and breaking promises just to get from one day to the next. But the peculiarity of our political system notwithstanding, Netanyahu needs to stop hemorrhaging his credibility if he is to provide the leadership these times demand.