Tonight was a very good night for the Republicans, as they were victorious in Congressional special elections that were held both in New York and Nevada. The New York race was nothing short of an upset of Scott Brown proportions, so we will focus on that race today.

In New York City, Republican Bob Turner was the surprise victor in this open seat. With 85% of the vote in, he leads 54-46%, but since the bulk of the remaining vote is in the more conservative precincts of Brooklyn, we project that he will ultimately win with 55%. This is a heavily Jewish Congressional district that elected Democrat Chuck Schumer for 18 years, and Democrat Anthony Weiner for 13 years after that. In other words, a district that Republicans only carried in Republican landslide years like 1972 and 1984. Furthermore, at the Congressional level, this district hasn’t voted for a Republican since 1923.

While it’s tempting to pass this off as an isolated special election victory, this election in fact has been part of a consistent trend away from the Democrats relative to the percentage of the vote that President Obama got in 2008. This drop-off in support, which we have referred to as the “Obama plunge” (explained in more detail here ), manifested itself starting with Republican victories in “blue” states like New Jersey, Virginia, and Massachusetts. It was Scott Brown’s upset victory in Massachusetts, in fact, which foretold massive GOP gains in the midterm elections.

The GOP upset in a heavily Jewish district in New York City, however, points to structural problems President Obama will have with getting re-elected, since his performance was the overriding issue in the race. Contrary to what pundits believe, the “Obama plunge” has not disappeared since the 2010 election: in fact, it showed up again in a special election in California this summer, where a Democrat won with 55% in a 64% Obama district. In this district in New York City, President Obama received 55% of the vote in 2008, so a Democrat’s getting a projected 45% of the vote points to a consistent “Obama plunge” of 10% in two different elections on two different coasts.

Practically speaking, what does a 10% “Obama plunge” mean? Keep in mind that the “Obama plunge” varies depending on the demographic makeup of the district. We noted back in the spring of 2010 that districts containing significant numbers of minorities, academics, and Jewish voters did not show an “Obama plunge” as deep as a district in the Midwest, for example. And in the case of New York, a 10% “Obama plunge” probably does not put that state in play for the Republicans in 2012 – indeed, no Republican has carried that state since the 1984 Reagan landslide, and even then, President Reagan only got 54% of the vote.

Where the “Obama plunge” DOES make itself apparent, however, are in the states that President Obama carried by respectable (but not landslide) margins. In other words, states like Colorado, Minnesota, Ohio, Michigan, and Pennsylvania are very shaky for the President right now, and about all he can count on would be Democratic bulwarks like California, Illinois, New York, and Massachusetts. So unless the economy significantly improves, or President Obama changes his tactics, he faces an unambiguous defeat on the scale that only former President Jimmy Carter would have experienced in 1980.