Just noticed this: Only 1 of the deep South states has a senate election this year while every Northeastern state except 1 has one. The Democrats are favored to cut into their deficit this year by at least 1 seat and could gain as many as 4 while I'm sure the Republican party would be overjoyed to just break even.
Even though the Republicans have a clear majority in the Senate, there are fewer Republican senators(16) up for reelection than Democratic ones(17). The election is 8 months out, but the Republicans really need some things to go their way just to maintain status quo. By the numbers, this year is their opportunity to open the gap and get that 60-40 majority. If the Democrats gain 3 seats this year, that would be monumental since in 2008 and 2010 combined(given the current makeup of the Senate) there will be 27 Democrats and 38 Republicans up for reelection.
How did this happen?
It's only 15 Republican seats. In addition to the 17 Democratic seats, there's Jeffords' open seat, where one IINO will be replaced with another IINO.