One of the better ways to judge where the people paid to maintain seats in Congress think things are going is by monitoring the campaign spending by the leading political committees. Their judgments are not always correct – the $3 million to Tammy Duckworth in 2006 is a good example – but because candidates often need the outside support, where the money is going, and especially where it’s NOT going, makes a difference.

So what can we learn from this? In the Senate, you can see the battleground shape up based on the seats where spending is happening.

Eight states are emerging as the battlegrounds that will decide the margin of Senate control, according to interviews with Republican and Democratic strategists.

They are Colorado, Illinois, Kentucky, Missouri, Nevada, Pennsylvania, West Virginia and Wisconsin.

Republicans need a net gain of 10 seats to win control of the chamber.

This matches up with where the committees are spending their money. The NRSC pulled out of California, tacitly conceding the seat to the Democrats, and they don’t plan to do much in Delaware (the DSCC’s still spending there). Similarly, the DSCC has given up on North Dakota, Indiana and Arkansas, and don’t look to be competing for GOP-held seats in Ohio, Louisiana, Florida, New Hampshire or North Carolina.

So if the Republicans sweep the above seats, that gets them to 50 (two of those above are currently held by the GOP). Republicans would have to put one more seat in play – perhaps Connecticut, where the DSCC is reportedly spending money, or Washington, where the NRSC has funds appropriated, or the aforementioned California. But the NRSC has raised less money than the DSCC, so they may not be able to expand the map as much as they want.

There was thought that the DSCC would pull out of Kentucky, but they were unfounded.

You also have to look at the spending from outside groups, which has been particularly large for Republicans in Nevada, Pennsylvania, Colorado, Kentucky and Missouri. That suggests that those should stay on the board as toss-ups, for now.

What about the House? That’s a little trickier, but Aaron Blake looked at some early ad buys there:

The National Republican Congressional Committee has now bought ad time in 31 districts, while the Democratic Congressional Campaign Committee has bought time in 24. The NRCC has spent nearly $6 million as compared to $3.7 million for the DCCC.

The NRCC and DCCC have also reserved time in 55 and 67 districts, respectively, but reserving time is not the same as actually buying it since money can be moved almost until the moment the ads are scheduled to run.

For the most part, the seats considered most vulnerable to switching parties are being ignored by both sides — a sign that they may well be lost causes. Most of the districts targeted thus far are considered second-tier pickups — the seats that will almost certainly make the difference between Republicans winning 39 seats, and not.

Blake notes that the DCCC and the NRCC are on the air in the same district in 12 cases: The districts are: MI-07 (Schauer), PA-11 (Kanjorski), AL-02 (Bright), PA-03 (Dahlkemper), MO-04 (Skelton), MS-01 (Childers), SC-05 (Spratt), MI-01 (Stupak – open seat), WI-07 (Obey – open seat), WA-03 (Baird – open seat), IL-10 (Kirk – open seat) and IL-14 (Foster). Those can be seen as the battlegrounds for both parties, and only one of the 12 is currently held by a Republican.

Blake further notes that the other seats, where the DCCC or the NRCC is on TV separately, aren’t even seen in the top 20 of seats most likely to switch. In other words, several Democratic seats (and a few Republican seats) are already seen as lost causes. Six seats – IN-02, VA-09, KY-06, NC-07, NY-23 and NJ-03 – have Republicans on TV even though the seats don’t fall among the top 50 most likely to switch by Blake’s measurements. So the NRCC is definitely trying to expand the map while putting away the low-hanging fruit.

Blake concludes:

While ad buys are a very good indicator of where the most competitive races are, they aren’t always foolproof, and shouldn’t be seen as the end-all, be-all in determining the state of the play in the House.

At the moment, Democrats seem resigned to significant seat losses — choosing to focus their money on three dozen or so races on which their control of the majority almost certainly rests.

As the Democratic undecideds potentially come home, this landscape could improve for Democrats somewhat. But follow the money and you’ll know a big part of the story.