Most of the Democratic fretting thus far in the election season — and with nine months to go it's still early on — has been focused on potentially losing their 39-seat majority in the House. After all, Democrats control the Senate, where incumbency rules, by a comfortable ten votes, and only 37 seats are up for grabs this year. However, recent retirements, worrisome poll numbers for several incumbents and the entrance of some strong GOP challengers have prompted a wave of concern amongst Senate Dems. While still unlikely, if a perfect political storm were to occur, there is a chance Democrats could lose the Senate. Here's what would need to happen:

Open Seats Likely to Switch:

At least two seats are all but write-offs for Democrats: North Dakota and Delaware. Delaware Attorney General Beau Biden's decision not to run for his father's old job means Dems have lost their best hope at keeping the seat from the popular, eight-term moderate Republican Congressman Mike Castle. And Byron Dorgan's retirement opens up a blue seat in a red state in a year that's trending red: Dems had no better candidate than the three-term Dorgan, who felt that even he couldn't win in this climate. "North Dakota is pretty much gone and Delaware has become very difficult," says Jennifer Duffy, Senate editor at the non-partisan Cook Political Report, which tracks congressional races. "This gets Republicans to 43."