5 Key Senate Races to Watch on Election Night

Colorado Sen. Bennet is struggling to hold onto his seat.

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Recent polls keeping tabs on key Senate matchups show clear trajectories for Republicans in Arkansas, Florida, and Kentucky and for Democrats in Connecticut, Delaware, and even California. But while these once competitive races become more defined, others in Colorado, Illinois, Nevada, Washington, and West Virginia have been consistently pegged by pollsters as virtual dead heats. And in a midterm election that is expected to dramatically alter the political landscape on Capitol Hill, the results of these five races will shape the makeup of the Senate.

[See photos from the campaign trail.]

In Colorado, Democratic Sen. Michael Bennet is struggling to hold onto his seat against Republican Weld County prosecutor Ken Buck. Bennet was appointed in 2009 by Gov. Bill Ritter after the seat was vacated by Interior Secretary Ken Salazar. Buck has consistently pegged Bennet as a Washington insider who supported Obama's stimulus package among other policies. Bennet has painted Buck as a radical who rode through his Republican primary on the back of the Tea Party movement. Polls show the race in a statistical tie. Voters in Colorado, a traditional bellwether and swing state, backed Obama in 2008 but supported Bush in 2004. Two years ago, roughly a third of voters were not registered with either party. And in a race this close, those independents could make all the difference. [See who is donating to Bennet.]

Meanwhile, the race for Obama's old Illinois Senate seat is up for grabs. Five-term lawmaker Mark Kirk and State Treasurer Alexi Giannoulias are virtually neck and neck, though Kirk has a slight edge of less than two percentage points. Both candidates have come under fire during the campaign for either gaffes or troublesome pasts. Kirk admittedly exaggerated his military record while Giannoulias had to defend the failure of his family-owned bank in Chicago. But neither candidate is particularly well liked; both have been polling below 40 percent in terms of voter favorability. A win by GOPer Kirk would represent a significant loss for Obama, who not only held the seat but also won the state in 2008 by 25 points. His approval rating there is 45 percent, according to a survey by the Democratic firm Public Policy Polling.

Another statistically tied race with a Republican edge is between the most powerful lawmaker on Capitol Hill and a Tea Party-backed former state assemblywoman. In Nevada, Republican Sharron Angle and Senate Majority Leader Harry Reid are virtually tied, though Angle narrowly leads the four-term Senator by a point. Independent voters, who made up roughly 20 percent of the electorate in the 2008 election, will play a significant role in the state's midterms. Nevada has the nation's highest unemployment rate, clocking in at 14.4 percent according to the latest Bureau of Labor Statistics report, and has been a victim of the housing market collapse. Voters in the state, like they did in Colorado, supported Obama in 2008 but backed Bush in 2004. [See where Reid's campaign cash comes from.]

But Democrats have a slight edge in the virtually tied race between three-term Sen. Patty Murray and Republican Dino Rossi in Washington, where Murray leads by nearly a percentage point. In Washington's open primary, the two candidates with the most voters advance to the state's general election, no matter their party affiliation. Murray edged Rossi 46 percent to 34 percent in the August primary, but the race has narrowed since then. Rossi has already lost two bids for governor while Murray has been voted into the Senate with no less than 54 percent of the vote in her past elections. Still, she is the fourth ranked Democrat in the Senate who helps to shape the party's agenda, making her a sizable target for Republicans. [See who is giving money to Murray's campaign.]

And in West Virginia, popular Democratic Gov. Joe Manchin and Republican businessman John Raese are running statistically even, though polls over the past couple of days have started to show Manchin with the edge. But the governor, who enjoys a job approval rating of roughly 70 percent in the state, has had to spend time and energy distancing himself from Obama, whose approval rating in West Virginia is among the lowest in the country. The healthcare reform law is unpopular in the state, which backed Republicans in the last two presidential elections. Whoever wins Tuesday will replace the late Democratic Sen. Robert Byrd, who during his half century in the Senate was known for bringing government projects back to West Virginia.