The charts above reflect the current voter preferences for the senate races in New Jersey, Mississippi, and Louisiana. They show the Democrat is favored in one race, the Republican in another, and the third race could be very competitive.
The race favoring a Democrat is in New Jersey, where the incumbent (Cory Booker) has a 20 point lead over his Republican opponent. It is going to be very difficult for the Republican to even be competitive in this race -- let alone win it.
In Mississippi, the incumbent Republican (Thad Cochran) looks to be in pretty good shape -- leading his Democratic opponent by 12 points. The only real hope is that the teabaggers in that state stay mad at Cochran for appealing to Blacks to beat their favorite candidate -- and either vote for a third party or stay at home on election day. If they come home to the GOP (as expected), then Cochran will probably win pretty easily.
The race in Louisiana looks good for Democratic incumbent Mary Landrieu, but we need to remember that all three of her opponents are Republicans. Unless she gets over 50% of the vote, there will be a runoff -- and the supporters of the two losing Republicans will probably support Landrieu's surviving Republican opponent, which would tighten the race up considerably. I still think Landrieu will eke out a win in Louisiana, but it is not going to be as easy as Booker or Cochran.
In the final analysis, I don't think these three states will change the balance of power in the United States Senate.
The Monmouth University Poll was done between June 25th and 29th of 800 New Jersey adults, and has a 3.5 point margin of error.
The Rasmussen Poll was done on June 25th and 26th of 750 Mississippi likely voters, and has a margin of error of about 4 points.
The survey from Public Policy Polling was done between June 26th and 29th of 664 Louisiana registered voters, and has a 3.8 point margin of error.