Even if you only peruse this space once in while—which makes sense because I only post once in a while—you know that I have urged readers to pay attention to Senate races this fall.

I return to that theme today because so much of the election oxygen is being consumed by the presidential race. Speculation about when Hillary Clinton will drop out of the Democratic primary and whether she will become Barack Obama’s running mate is the latest obsession consuming the top of the ticket.

Prognostications about John McCain’s longevity likely will fill up the airwaves and cyberspace this weekend now that the Arizona Republican has released his health records.

But dig a little deeper into the ballot this fall and you will get to races that will go a long way in determining the fate of labor law in the next Congress. Specifically, watch the Senate races where open seats or vulnerable Republicans are juicy prey for a hale and hearty Democratic Party.

Currently, the Senate is comprised of 51 Democrats and 49 Republicans. But many of the most contentious issues in that body are not decided by a simple majority vote.

Instead, they are subject to cloture, or a requirement of 60 votes in order to end debate and move to a vote on final passage of a bill. Failure to invoke cloture means that a bill has been filibustered.

There’s no doubt that the GOP will lose Senate seats this fall. The only question is how many. The closer they get to 40, the less power they will have to filibuster.

This is important for labor law because a couple of prominent measures in that area have been filibustered. But in a simple majority vote, they would have been approved.

For instance, there is the Employee Free Choice Act. It would allow a union to be recognized when a majority of workers sign cards authorizing one. Under the measure, companies could not insist on a secret ballot election supervised by the National Labor Relations Board.

The so-called card-check bill failed to gain cloture last summer, 51-48. Some of the senators who filibustered that measure are among the most endangered Republicans up for re-election.

That group includes Sens. Susan Collins (Maine), Norm Coleman (Minnesota), Elizabeth Dole (North Carolina), Gordon Smith (Oregon), and John Sununu (New Hampshire). In addition, Sen. Pete Domenici of New Mexico voted to stop the card-check bill. But he is retiring and the race for his seat will be highly competitive.

The filibuster math changed a bit on a labor law vote last month. The Senate failed to invoke cloture on a measure that would have made it easier for workers to sue for pay discrimination. The Senate filibustered the Lilly Ledbetter Fair Pay Act of 2007 by a 56-42 tally, four short of the magic 60 to end debate. 

The number of votes for cloture would have totaled 57 except that Senate Majority Leader Harry Reid, D-Nevada, changed his vote in order to be able to bring the bill up again later this year. Two senators—Chuck Hagel, R-Nebraska, and McCain—did not vote.

If you assume that Hagel and McCain would have been in favor of the filibuster, it would have been upheld by 43 votes. That leaves Republicans with a fairly narrow margin, as they look ahead to battling the bill again in the next Congress.

The political calculus on Ledbetter is a little different than it is on card check. Collins, Coleman, Smith and Sununu all voted in favor of ending the debate on Ledbetter. Of the senators listed above, only Dole voted to filibuster Ledbetter.

But the point remains that as Republicans slip toward 40 total senators, their ability to filibuster will diminish. Depending on where you stand on issues like the card-check and Ledbetter bills, you may find that encouraging or discouraging.

The vulnerable Republicans are likely happy that McCain is the Republican presidential nominee. Like him, they are moderates. It will help their cause to have him at the top of the ticket.

But if they and McCain lose in November, Democrats are in a much stronger position to get measures they support signed into law. In Washington, there will be a House and Senate with larger Democratic majorities and a Democrat in the White House.

The only thing standing in the way of the card-check and Ledbetter bills becoming law will be somewhere around 43 Republican senators. Keep your eyes on the Senate races this fall.