Former Alaska governor Sarah Palin shakes hands with supporters as she joins U.S. Sen. Pat Roberts for a pancake breakfast at the Independence Historical Museum and Art Center on Thursday, Sept. 25, 2014 in Independence, Kansas. Roberts is locked in a close race with independent challenger Gregg Orman. (AP Photo/The Wichita Eagle, Jaime Green)

The fight for the Senate majority is increasingly focused on five races: four controlled by Democrats and one held by Republicans. These contests -- Alaska, Colorado, Iowa, North Carolina and Kansas -- are acknowledged by both sides to be very competitive, and because of that are likely to see the heaviest spending by both the party committees and the outside groups over the last five-plus weeks of the midterm election.

Of the quartet of Democratic seats, North Carolina -- somewhat amazingly -- looks to be the toughest pickup for Republicans. Sen. Kay Hagan (D-N.C.), thanks at least in part to a spending edge on television over the last month or so, has managed to build a steady four-ish-point edge that state House Speaker Thom Tillis (R) has been unable to narrow. Republicans feel increasingly positive about Alaska -- where the Chamber of Commerce released a poll this week showing Dan Sullivan (R), whom the group has endorsed, ahead of Sen. Mark Begich (D) by six points -- and Colorado, where three straight polls show Rep. Cory Gardner (R-Colo.) ahead. Iowa is, today, the purest toss up race in the country.

But for Republicans, Kansas has become a major headache. Sen. Pat Roberts (R-Kan.), having survived a contested primary in August, seemed to think reelection to a fourth term was ensured and stopped doing, well, much of anything. Meanwhile, independent businessman Greg Orman was spending seven figures on an August media buy that boosted him significantly. Democrat Chad Taylor's decision to drop out of the race -- and the subsequent legal ruling that his name could be removed from the ballot -- further endangers Roberts by coalescing the anti-Roberts vote. Roberts's allies insist the senator now finally understands the peril he is in and has been aggressively raising money since Labor Day. They also believe tying Orman to Democrats (he ran for the same seat as a Democrat in 2008) and unearthing his various business ties will make the last five weeks much harder for him than the previous five weeks.

The rest of the competitive Senate races seem to be moving in a clear direction. Democratic pickup chances in Kentucky and, to a lesser extent, Georgia seem to be fading. Democratic open seats in Montana, South Dakota and West Virginia are gone. Democratic strategists are growing increasingly pessimistic about their chances in Arkansas and Louisiana. Scott Brown increasingly has a chance in New Hampshire, but it's hard to see him winning before any of the four Republican candidates running in Alaska, Colorado, Iowa and North Carolina.

Add it all up and you get a Republican Party teetering on the edge of a majority -- needing six seats and with at least five either in the bag or leaning their way. The five seats mentioned above are the majority makers -- or breakers. Republicans need two of the five. Keep your eye on them.

Below are the 13 seats most likely to change hands on Nov. 4.  The No. 1 race is considered the most likely to switch parties.

13. Kentucky (Republican-controlled): Alison Lundergan Grimes' (D) gun ad backfired on her. Envisioned as a way to put distance between herself and the unpopularity of President Obama, the ad was trumped by a commercial McConnell ran a day later using footage of the president, like Grimes, skeet-shooting. McConnell is well on his way to doing what he has always done in campaigns: Villainizing his opponent to the point that voters, who are hardly enamored with him, decide he is the better option. (Previous ranking: 11)

12. New Hampshire (Democratic-controlled): A new entry on our list, it's hard to ignore the polls that show former senator Scott Brown (R-Mass.) closing the gap on Sen. Jeanne Shaheen (D-N.H.). CNN/Opinion Research showed the race tied, while the latest Granite State poll showed Shaheen up just two. Other polls show the gap wider, though, so it's hard to move this one too far up our list just yet. Also: Shaheen is more popular than most folks on this list, so for Brown, getting over the hump could prove a little more difficult. (Previous ranking: N/A)

11. Georgia (R): Businessman David Perdue (R) has led in most recent polls and got a boost when George H.W. Bush officially endorsed him, since Democrat Michelle Nunn has emphasized her connections to the former president in an effort to boost her centrist credentials. Ever since Nunn's campaign strategy documents leaked over the summer, she has not looked quite so formidable. But while most polls remain close, and she has time to turn things around, it's clear she's the underdog. (Previous ranking: 9)

10. Colorado (D): The last three polls in this race all showed Rep. Cory Gardner (R-Colo.) leading, with two of them being within the margin of error. The latest was Democratic-leaning automated pollster Public Policy Polling, which showed Gardner up two on Thursday. We've been a little slow to label this one a toss-up, but the evidence is certainly pushing it in that direction. (Previous ranking: 10)

9. North Carolina (D): Of the four Democratic senators running for reelection in states Mitt Romney won in 2012, Hagan is right now the likeliest to win. But her race against state House Speaker Thom Tillis (R) is very close. Both parties have already pumped heaps of cash into this race, but the GOP spending mostly came early, and Hagan is benefiting from more backup right now. Hagan's survival could rest on the strength of the Democratic ground game -- particularly when it comes to getting African Americans to the polls. (Previous ranking: 7)

8. Iowa (D): It's close. Very close. The Real Clear Politics poll of polls in the race gives state Sen. Joni Ernst (R) a 0.2 percent edge over Rep. Bruce Braley (D), which statistically speaking means this is a total jump ball. Ernst is the better candidate, but Braley benefits from the state's slight Democratic lean. This is the race of the cycle right now. (Previous ranking: 8)

7.  Kansas (R): The ballot is set here, and there is no Democrat on it. That's good news for independent Greg Orman. The question now is whether he can maintain his standing in the polls in the face of a renewed GOP effort to take him down. His ace in the hole is the continually uninspiring candidacy of Sen. Pat Roberts (R-Kan.), which is what got us to where we are in the first place. Until Roberts rights the ship, this is moving up our list. (Previous ranking: 11)

6. Alaska (D): A campaign that has recently focused on snow machines and frostbite looks like it could very well be the decisive race for control of the Senate. Data is scarce in Alaska, but the last four public polls all show former attorney general Dan Sullivan (R) leading Sen. Mark Begich (D-Alaska). This is looking more and more like the sixth GOP pickup. (Previous ranking 6)

5. Arkansas (D): This race has swung back and forth like a pendulum. First, it looked like Sen. Mark Pryor (D) was a goner no matter what he did. Then came a series of polls showing him holding his own or leading. Those raised some concerns about whether Rep. Tom Cotton (R), still a relative political newcomer, was up to the challenge. Now, it appears the Republican has regained his footing and is the clear favorite. (Previous ranking: 5)

4. Louisiana (D): This one isn't being written off just yet, but a Fox News poll last week showed Rep. Bill Cassidy (R-La.) leading Sen. Mary Landrieu (D-La.) by 13 points in a likely runoff, 51-38. If that's even close to accurate, Landrieu is in big trouble. And we hate to ascribe political motivations to every little thing a politician does, but a sitting United States senator participating in a keg stand doesn't feel like something you do if you feel good about your political standing. (Previous ranking: 4)

3. South Dakota (D): Former governor Mike Rounds (R) is firmly in control of this race, polls show. Democrat Rick Weiland has never really made a move. The wild card here is Larry Pressler, a former Republican senator running as an independent. Despite his GOP past, Pressler is probably a bigger hindrance to to Weiland. (Previous ranking: 2)

2. West Virginia (D): Rep. Shelley Moore Capito (R) is coming to the Senate. Democratic Secretary of State Natalie Tennant has been a fine candidate, but this race, for her, has always been about setting herself up for a more advantageous contest down the line. (Previous ranking: 3)

1. Montana (D):  Sen. Steve Daines (R). (Previous ranking: 1)