|Linda Lingle via Wikipedia|
|Connie Mack IV via Wikipedia|
|Robert Menendez by Getty Images via @daylife|
|Image via Wikipedia|
|George Allen via Wikipedia|
Democrats now have 53 seats in the 100-member chamber, including two held by independents who usually caucus with them. Almost half of these seats are being contested at the same time as the presidential election on November 6, 2012, with more than 20 defended by Democrats.
Here are some races that could tip the balance.