JUDY WOODRUFF: And we turn to politics, but not the presidential campaign. Instead, we focus on what we're calling the Senate six.
Ray Suarez has that.
RAY SUAREZ: If Republicans capture four Senate seats, they will gain control of the chamber. So, the "NewsHour" has chosen six key races to follow in the coming months, ones we think will serve as a guide to the battle for the majority this fall.
And political editor Christina Bellantoni is here to explain which contests we have selected and why.
And, Christina, we should remind people that in every two-year cycle, a third of the Senate comes up. So out of these 33 seats coming up in the fall, how many are held by Democrats and how many by Republicans?
CHRISTINA BELLANTONI: Republicans are only defending 10 seats, and the Democrats are defending 23 seats, which is what happens in the cycle six years after you have won a giant wave election year.
In 2006, the Democrats took over the Senate, in part because of races in some of the more traditional red states, Montana, Virginia, et cetera. So a lot of those seats are now on defense. Plus, you have a lot of retirements which are shaking up the map.
So one of the reasons we laid out the Senate six on our Web site today was just take a look at where we're going to see this battle play out over the fall, how it's going to tell the story about the national picture.
There are a few seats. The Republicans, as you noted, only need those four. You have got Nebraska and North Dakota that could very well flip to the Republicans. These are Democrats who are retiring from those seats. They're trending to be more conservative states. So that's already two seats down.
Missouri is a very tough state for Sen. Claire McCaskill, a Democrat who won in 2006, defending there. So we have picked these races to really look at where we're going to be able to tell if Senate control is actually up for grabs in the fall.
RAY SUAREZ: So we will take a quick run through the Senate six going from west to east and starting in Nevada. Tell us about it.
CHRISTINA BELLANTONI: Yes.
So in Nevada, you had Sen. John Ensign step down from his seat after a host of ethics issues there. And he's a Republican. And he was replaced by Sen. Dean Heller, who was a member of Congress. This was always going to be a seat that Ensign was going to just retire. So Heller had his sights on that seat. Shelley Berkley, also a member of Congress from the Las Vegas area, is running as the Democrat there.
What's interesting about Nevada there is, this is a presidential battleground state. And particularly the Obama campaign has put in a lot of resources to make sure they have the get-out-the-vote operation in check, to make sure they can target Latino voters, and to really, really activate the Harry Reid machine there. This is Harry Reid's home state. And he's going to be going after this seat.
RAY SUAREZ: Next, Montana, where incumbent Jon Tester took the seat in a squeaker of an election in '06. What's the dynamic there?
CHRISTINA BELLANTONI: Well, this is a very interesting race too. Tester has only served for one seat -- one term, and he's running against Denny Rehberg, who is the Congress member there.
They run at large in Montana because it's such a slim population there. So Denny Rehberg has been winning statewide already for a decade. So this is going to be a very competitive race locked from the very beginning to the very end. It's also a state where it's cheap to buy advertising. So expect to see a lot of ads there.
RAY SUAREZ: Next, New Mexico, an open seat with the retirement of Jeff Bingaman, a kind of purple state. They elected a Republican governor in 2010, but went for Obama by 15 points in '08.
CHRISTINA BELLANTONI: Yes. This is a better seat for the Democrats. They are probably going to hold it.
But there is a competitive Democratic primary for the nomination there. And Heather Wilson, a former member of Congress from New Mexico, is running for the Republican nomination. And, at first, people thought she would be challenged from the right and she would be dispatched, because that's what happened actually a few years ago. She lost in the Senate primary.
But she looks to be the nominee there, and Republicans are very confident that she can do well this fall.
RAY SUAREZ: Another open seat in Wisconsin with the retirement of veteran Herb Kohl, what is going on there?
CHRISTINA BELLANTONI: So you have got Tommy Thompson, former Bush administration official, former governor, is likely to get that GOP nomination. They haven't selected that yet. And he's likely to face Congresswoman Tammy Baldwin, who is running to be the first openly lesbian senator in the country.
And so that is going to be a very close race. This is a very important battleground state in the presidential election. And obviously there's a lot of attention because of the governor's recall that's going to be this summer with Governor Scott Walker there. He's a Republican.
RAY SUAREZ: In Virginia, one of the longest of the long nights in 2006, but Jim Webb decided not to fight to keep his seat. Another open one.
CHRISTINA BELLANTONI: Yes, that's right.
And Virginia always takes on a bit of national implications, in part because it's in Washington, D.C.'s backyard, but also because you have got big personalities there and you have got Tim Kaine, former governor, former Democratic National Committee chairman, one of Barack Obama's best friends, who is running for the Democratic ticket there.
And then George Allen, the former senator who Jim Webb unseated in 2006, wants his seat back. He obviously still has national ambitions. So this is a lot of money that is going to be involved in this race, and it's a very important battleground state for the Obama campaign.
President Obama needs to win Virginia to win reelection. So they're pouring a lot of resources there. And it's sort of one of those states where if Obama, Mr. Obama does well, you're going to see Tim Kaine probably do well, but it will be very close.
RAY SUAREZ: Well, if you want to continue to talk about money, Massachusetts is next. Outside money is pouring into that state, isn't it?
CHRISTINA BELLANTONI: Yes, this is another one with national implications.
Senator Scott Brown won the surprise special election after Sen. Ted Kennedy passed away. And he was really this vote against health care reform and looked at as this Republican savior, the new face of the party. But he's also voted sort of along the lines of Massachusetts. He's been a little bit more independent. He voted for the repeal of don't ask, don't tell. So he's remained pretty popular there.
But Democrats very much like their chances with Elizabeth Warren, Harvard Law School professor who has worked with President Obama. They think she can raise a lot of money. She's got more than $7 million in the bank. This is a big deal there. And it's a state where Democrats have an advantage. So if President Obama does well there, you have got probably a good night for her, which means the Democrats are taking over a seat in that case.
RAY SUAREZ: But seesawing opinion polls early, right?
CHRISTINA BELLANTONI: Yes, absolutely. And they're fairly close. And you have seen a lot of change here.
Warren was leading. Now they're pretty closely matched.
RAY SUAREZ: And we have got time for a bonus state.
CHRISTINA BELLANTONI: Yes, exactly.
RAY SUAREZ: Maine, which came as a surprise that it was even going to be in play. But Olympia Snowe retired.
CHRISTINA BELLANTONI: Yes. So Olympia Snowe was known as a moderate independent type Republican, but this is a Republican seat. So the Democrats were very excited, hoping that their candidate would run.
They didn't really get anyone marquee. So what happened instead was former two-term Gov. Angus King is actually running there. And he's being very coy about what whether he will caucus with the Republicans or the Democrats, because, potentially, if you have a split chamber, he could be a real kingmaker in party control.
So we are going to be watching this closely as sort of a bonus race. We should point out that King said he is going to vote for President Obama in the fall, so that gives you one indication of where he's headed.
RAY SUAREZ: Christina Bellantoni, thanks a lot.
CHRISTINA BELLANTONI: Thank you.
RAY SUAREZ: There's another Senate race. We will examine veteran Republican Dick Lugar, who is facing a challenge from his right. Gwen Ifill reports on that primary fight tomorrow night.