In Indiana, a state once key to a Republican majority, chances look less favorable for the party as a gaffe from GOP candidate Richard Mourdock has damped his odds. In Missouri, Rep. Todd Akin (R ) has made up some ground but there are questions as to whether he can recover from his controversial remarks on rape.

And, in Nebraska, Democrat Bob Kerrey suddenly looks capable of mounting a come-from-behind win against Republican Deb FischerDebra (Deb) Strobel FischerBill to bolster gun background checks gains enough support to break filibuster Senate Republicans call on Trump to preserve NAFTA US trade deficit rises on record imports from China MORE, though he faces an uphill battle in the red-leaning state.

A recent independent poll, the first since September, showed him closing his gap substantially and lagging Fischer by just 3 points. The sudden opening in the race inspired an influx of outside spending, with Crossroads GPS launching a $420,000 ad buy to shore up their bet, while independent group VoteVets Action Fund spent $300,000 on ads attacking Fischer this past week.

Kerrey also rolled out the endorsement of former GOP Sen. Chuck HagelCharles (Chuck) Timothy HagelIntel chief: Federal debt poses 'dire threat' to national security Hagel: Trump is 'an embarrassment' Tax cut complete, hawks push for military increase MORE, a revered political figure in the state, as part of a last-minute push for support.

It remains a long-shot — Fischer formerly posted consistent double-digit leads on Kerrey, and Mitt Romney leads President Obama by a similar margin — but Kerrey's mounting an improbable challenge in the final days of the campaign, and The Hill has moved the race from Likely to Lean Republican.

These ratings and projections will be updated throughout the campaign cycle. The full Senate ratings are below. Ratings for the House are available on The Hill’s Ballot Box blog under the Race Rating category.

The Hill's 2012 Race Ratings: Senate

Likely Democratic Lean Democratic Toss-up Lean Republican Likely Republican
HI: OPEN (Akaka)CT: OPEN (Lieberman)AZ: OPEN (Kyl) NE: OPEN (Nelson)
MI: Stabenow (D)FL: Nelson (D)IN: OPEN (Lugar)

MN: Klobuchar (D)MA: Brown (R)MT: Tester (D)
NJ: Menendez (D) ME: OPEN (Snowe)**NV: Heller (R)    
WV: Manchin (D)  MO: McCaskill (D)ND: OPEN (Conrad)    
  NM: OPEN (Bingaman)VA: OPEN (Webb)    
  OH: Brown (D)WI: OPEN (Kohl)    
  PA: Casey (D)     
*Bold indicates a seat projected to switch parties.
**Former Maine Gov. Angus KingAngus Stanley KingLindsey Graham: Trump firing Mueller would 'probably' be impeachable offense Angus King: McCabe firing seemed 'mean-spirited' With bills on the table, Congress must heed the call to fix our national parks MORE (I) is expected to caucus with Democrats if elected.