The victory of Robert “Bob” Turner in the race to replace Rep. Anthony Weiner in New York’s 9^th Congressional District hands the Republicans a seat that the Democrats would, according to most polls, have held had Mr. Weiner stood for reelection.

The 9^th is a district with a three-to-one Democratic edge among registered voters and a heavy Jewish population that can be counted on to turn out in impressive numbers in most elections. Despite this, one Democrat, Mayor Koch, saw this as a unique opportunity to “send a message” to President Obama, who many think is shifting American support away from the Jewish state.

Mr. Koch endorsed the Republican, Mr. Turner, and helped to make him an improbably credible candidate in a district considered impossible for a Republican to win. The result will be felt in Washington, right up to the White House, and could well contribute to a change in American policy.

If so, it couldn’t come at a more critical time for Israel, faced with existential threats from its enemies. And it won’t be the first time that a special election to fill a vacant New York Congressional seat might have had a major effect on American policy towards Israel.

In 1947, Congressman Benjamin Rabin of the Bronx, resigned his seat, effective December 31, to assume a seat on the New York State Supreme Court. Today, becoming a member of the U.S. House of Representatives is considered by many to be the culmination of a political career. Back then, it was viewed as a stepping stone to other political jobs, even a spot on New York’s lowest court.

A special election was called for February 17, 1948. This was just months before the State of Israel declared its independence, and just about two months after the United Nations voted to partition Palestine into a Jewish and Arab state. With war on the horizon, the Jews of Palestine were suffering under an American arms embargo, and there was concern as to whether President Truman would recognize the Jewish state once independence was declared.

Leo Isacson, a former one-term Assemblyman who ran under the banner of the far left wing American Labor Party, quickly declared his candidacy for the vacant seat. Isacson was a committed Zionist, consistent with the support of the American left (as well as the Soviet Union) for a Jewish state.

The stakes were high. Isacson was backed by a former vice president, Henry Wallace, who was preparing his own run for president with the support of the ALP, a real threat to the president’s reelection prospects.

Wallace had a particular axe to grind here. The Bronx Democratic leader, the legendary Edward J. Flynn, was a major power in the national party and had been a confidant of President Franklin D. Roosevelt, who had recently died. Flynn lobbied to have Wallace dropped as the vice presidential nominee in 1944, which, as things turned out, would have put Wallace in the White House when Roosevelt died suddenly in April, 1945.

With Wallace’s strong support, Isacson ran a spirited race as the candidate of “Peace, Prosperity, and Palestine,” and won nearly 56% of the vote in a four-way race in the working class southeast Bronx’s 24^th District.

Taking his seat, despite the efforts of at least one Republican to have the House refuse to seat him because his “loyalty was in doubt,” he declared in his first speech on the day he took office, “I am a Jew!” Isacson fought the arms embargo against the Jews of Palestine, and the following day introduced his first bill, one which would “recognize the independent Jewish State in Palestine and guarantee its security against attack.”

All this could not have escaped the attention of the White House.

If Leo Isacson could beat the powerful Bronx Democratic Party over the issue of the Jewish State, this put the normally reliably Democratic Jewish vote in play. Certainly there has been much speculation as to the reasons for Truman’s quick recognition of Israel in May, but certainly the political lesson of the February 17^th special election in the Bronx was noted.

Isacson became the first (of many) members of Congress to visit Israel, at some personal risk of life and limb during the War of Independence. But back at home, the Jewish vote solidified behind the Democrats, who joined with the Republicans to defeat Isacson in the November election.

With Truman solidly behind Israel, Jewish support for Wallace melted away. Leo Isacson served less than a year in Congress, not much less that the winner of Tuesday’s election in Brooklyn and Queens is expected to serve before being reapportioned into oblivion. Isacson never won another office and died in 1996. But the lesson of his brief political career may well be reprised at this very moment.

Mr. Wolf is a contributing editor of The New York Sun.