The upset victory yesterday of Republican Bob Turner in the heavily Democratic and Jewish New York City congressional district that straddles Brooklyn and Queens – is a watershed moment that signals, I hope, the beginning of the end of Barack Obama’s presidency. Obama truly is vulnerable. He can be defeated.

The race was closely watched as a measure of attitudes toward President Obama. Republicans sought to channel voter discontent with Obama’s economic policies into a “referendum” on the Obama presidency.

The Jewish vote was a particular focus of attention. Former New York City mayor Ed Koch, a Democrat, urged voters to send a message of dissatisfaction to President Obama over his policies toward Israel.  This congressional district has the fourth-largest Jewish population of any congressional district, with some 173,000 Jews, and about a third of the district’s active voters are Jewish. Koch’s call seems to have had an impact.

Of course, Democrats like Representative Debbie Wasserman Schultz of Florida, the chairwoman of the Democratic National Committee, already are seeking to dismiss the relevance of the defeat, arguing that the district’s large concentration of Orthodox and Russian Jews make it unusual and that consequently the race has few national ramifications.

But she is either fooling herself of covering up for her side. The Democrats have always had a lock on the ninth congressional district, previously held by Anthony Weiner, even in the toughest economic times. They’ve held the seat for more than 90 years.

Moreover, the national Democratic campaign poured hundreds of thousands of dollars of advertising money into the race on behalf of Democratic loser David Weprin. Top Democrats pumped for Weprin. New York Gov. Cuomo and former President Clinton recorded automated phone calls to voters for Weprin, and NY Senator Schumer, who formerly represented the ninth district, campaigned with Weprin. Weprin himself is an observant Jew, a strong supporter of Israel, and a scion to a prominent family in the district. He still lost. Obama lost it for him.

For those who fear a second Obama term, this is good news. Obama is not invincible, even if the Republican line-up of presidential contenders still seems weak.

I don’t accept the contention that voters in the Turner-Weprin contest were beguiled by scare-mongers or that the vote was distorted by parochial community concerns such as Israel. I think it represents mainstream, healthy voter instincts, which recognize that Obama is clueless at best about repairing the American economy and is damaging to America’s standing in the world.

And when it comes to Israel, yes indeed, Jews are frightened about an extension of Obama’s term in office. For good reason. He has twice surprised Israeli leaders with problematic diplomatic initiatives relating to Israeli-Palestinian diplomacy, and his distaste for Netanyahu is palpable. He has nary a nasty word to say about obstinate and misguided Palestinian leadership, nor about loutish Syrian or Turkish leaders. It doesn’t appear that he doing much about stopping the Iranian nuclear drive either.

Churning inside just about every American and Israeli Jew that cares about Israel is the deep-seated fear that, freed from domestic constraints, a second-term Obama would make life for Israel extremely difficult. The Carter experience is instructive.

From memoirs published after he lost re-election in 1980, we now know that in 1978 then-President Jimmy Carter convinced Egyptian President Anwar Sadat to sign the Camp David accords – even though Sadat was not satisfied with them – by promising Sadat that he, Carter, would ‘deal’ with Israel toughly in his second term. One can only imagine what that would have meant.

Since then, Carter has revealed his true feelings about Israel in a long series of books and speeches, in which he has applied the apartheid label to Israel, called for talks with the Hamas, and generally added his name to very many unfriendly ‘human rights’ initiatives designed to isolate Israel.

Thank G-d that Carter was not re-elected! A second Obama term may present similar perils.