In Kentucky, Sen. Jim Bunning won in 2004 by just 1 percent. That could be a very close race again, which has Republican decision-makers urging Bunning to retire.

"Senate races -- more so than the House races -- recently have swung with the 'national mood' in elections," says Brown. "You saw Republicans pick up seats in 2002 and 2004, and Democrats pick up seats in 2006 and 2008."

Even if President Obama succeeds in working with Congress to pass legislation, the effects of those policies likely will not yet be felt by Americans in 2010. The public is more than likely to believe that, with Democrats in control, government isn't doing enough.

Barring another economic or foreign-policy crisis, the partisan pendulum is likely to swing once again, and Republicans will do better in 2010 than in the past two elections.

"The only two seats where I imagine that the Republicans will have a chance to take them will be Sen. Salazar's seat in Colorado and Reid's seat in Nevada," Brown says.

Now, knocking off Senate Majority Leader Harry Reid would be a moral victory for Republicans, similar to their defeat of former majority leader Tom Daschle in 2004. But that still won't get the GOP anywhere near a 51-vote majority.

Brown says to watch the special election in Illinois; lots of drama playing out there might help Republicans. Will scandal-era-appointed Democrat Roland Burris decide to run for a full Senate term? Will Burris be challenged by Rep. Jesse Jackson Jr.? What if special prosecutor Patrick Fitzgerald's investigation expands to include more Democrats besides Gov. Rod Blagojevich?

That may make Illinois in 2010 for Democrats similar to Ohio in 2004 for Republicans, when a governor's scandal felled nearly the entire GOP state slate.

For Republicans nationally, it all depends on recruitment. Luckily for them, retirements so far have come early enough to find quality candidates and to raise money.

Their fortunes largely rest on their relationship with President Obama and the Democrat-controlled Congress: Hold Democrats' feet to the fire, and Republicans could be called "obstructionists"; be too agreeable, and they'll be accused of playing "yellow-bellied roll-overs."