The control of the senate will come down to the following 13 races, and Democrats start out with a pretty high baseline of 44 seats since Debbie Stabenow in Michigan and Martin Heinrich in New Mexico should roll to easy victories.
Florida (Nelson +8) (based on 11 polls) - The median has remained constant all week, and the three polls releasing senate numbers this week showed Nelson beating Mack by 4 to 8 points. Mid-September was the last time a poll showed Mack winning, and that poll was an outlier by Gravis Marketing.
Ohio (Brown +7.5) (based on 12 polls) - All the polling attention in Ohio has been lavished on the presidential contest, mostly because Sherrod Brown pretty much has this thing locked up. "Only" five polls were released this week with senate numbers, and none of them showed a lead for Josh Mandel; Survey USA's 1-pointer from Wednesday seems to be an outlier.
Pennsylvania (Casey +6) (based on 9 polls) - One would expect polls' margins to be evenly scattered across a spectrum with outliers occupying both margins. This is still not the case in Pennsylvania, where most polls have Republican Tom Smith's support at or below 42%, except that Quinnipiac, Rasmussen and Susquehanna have his support at 45% or above. At least one group will be wrong on election day.
With the pretty sure bets in Florida, Ohio and Pennsylvania, Democrats will have 47 seats.
Massachusetts (Warren +4.5) (based on 8 polls) - Three new polls this week put Elizabeth Warren's support at an average of 50%, and it seems like she's starting to pull away. The median poll spread last week was only 3 points. Democratic seat number 48.
Connecticut (Murphy +3) (based on 7 polls) - There were four new polls in Connecticut this week: the two Republican-leaning polls said Murphy was basically tied with McMahon, while the two Democratic-leaning polls said Murphy was basically up by 5. One of those Democratic-leaning polls was a Quinnipiac poll (tilts D+1.4 in the presidential race) that had McMahon up by 1 on October 4th. Their latest shows a seven-point swing towards Murphy. This should be Democratic seat number 49.
Missouri (McCaskill +3) (based on 4 polls) - Right now the spread in Missouri is the same as in Connecticut, but the demographics of the state are light-years apart, and the trends are going in opposite directions. The new Mason-Dixon poll showing McCaskill only up 2 drove the poll spread down 3 points by itself. A note of caution: Missouri is pretty thinly polled. Right now this is Democratic seat number 50, which would give Democrats control assuming Barack Obama is reelected.
Wisconsin (Baldwin +2) (based on 7 polls) - Only two polls came out this week, and they both showed a race within the margins of error. The median poll spread for Baldwin dropped half a point this week. If Baldwin can hold on, this is the Romney-proof 51st Democratic senate seat.
Virginia (Kaine +2) (based on 8 polls) - Three polls in Virginia bothered to survey this blockbuster senate race this week. Two of them were Rasmussen and Gravis, so the median poll spread for Kaine dropped half a point this week. The Washington Post poll showing Kaine up by 7 is an outlier from one of the most Democratic-leaning outlets (D+2.6 in the presidential race). If Kaine can hold on, this is the Romney-and-Angus-King-proof 52nd Democratic senate seat.
Arizona (Carmona +1) (based on 3 polls) - Some other firm needs to poll this race, because we have polls from PPP and the weird outlier from a local firm defining this contest as a Carmona win. I am skeptical. This is the final race showing a Democratic lead currently in the median spread, the 53rd senate seat, a Romney-proof, Angus-King-proof, Joe-Manchin-proof Democratic majority.
Montana (tied) (based on 4 polls) - Another state in need of more polls, the only non-partisan poll that came out last week was from Pharos Research Group, which showed Democrat Jon Tester up two points. Right now Tester is only being held back by a Mason-Dixon poll from September or else he'd be the 54th Democratic seat.
Of the 13 senate battlegrounds, Republicans are currently ahead in only 3 of them.
Nevada (Heller +1) (based on 6 polls) - Three new polls this week, and two showed a tightening of the senate race in Nevada; the median spread slipped from Heller +5 to Heller +1.
North Dakota (Berg +3) (based on 4 polls) - Despite the addition of Pharos Research Group to the mix, this race could still use more polling.
Indiana (Mourdock +4) (based on 3 polls) - No poll has been taken since the Republican Mourdock's theological views on rape came to light, but as his view relies more on faith than junk science like Todd Akin's, it might not matter to Indianans.