Year one of the Obama administration ends Wednesday. Another era may come to an end the day before, when Massachusetts voters choose a senator to fill the three years remaining in the term of Edward Kennedy, who held the seat for 47 years.

If Republican Scott Brown wins that election -- and he seems to have an excellent chance to do so -- that election will mean the end, after just seven months, of the Democrats' 60-seat Senate supermajority.

That era began in July, when Al Franken was seated after protracted litigation over the result in an election in which both he and incumbent Republican Norm Coleman got an underwhelming 42 percent of the votes. And Franken was the 60th Democrat only because in the preceding April Arlen Specter, in his 29th year in the Senate and facing defeat in the Republican primary, switched parties for the second time in his political career.

Going back a little further, Democrats owed their 60 seats to the victories in 2006 of Jon Tester by 3,562 votes in Montana and Jim Webb by 9,329 votes in Virginia. In the 435 House races each year, close races tend to be split evenly between the parties. But in the 30-some Senate races in each cycle, a small number of votes can make a huge difference in the balance of power in that chamber.

So the Democrats' supermajority was the result of a series of happy (or unhappy, depending on your point of view) accidents. The same was true of the 55-45 majority the GOP held three years ago.

The very real possibility that the Democrats may lose their 60th seat -- and in Massachusetts, the only state George McGovern carried in 1972 -- suggests that it was perhaps not such a happy accident for them in the end.

Michael Barone is senior political analyst for The Washington Examiner and a Fox News contributor. To continue reading his column in The New Post, click here.