When the history books are written, this week may go down as a seminal point in the 2012 battle for control of the Senate.
Despite a multitude of vulnerable Democratic-held seats at the start of the cycle, it's increasingly possible that Republicans' inability to stem their own losses could allow Democrats to hold their narrow majority.
Sen. Olympia Snowe's (R-Maine) retirement immediately put an otherwise safe seat in jeopardy. Now, GOP-held seats in Maine, Massachusetts and Nevada ó three states President Barack Obama won by 12 points or more ó are in critical political peril, making the party's task of netting four seats more difficult.
Further complicating the GOP's path to 51 seats was former Nebraska Sen. Bob Kerrey's (D) announcement that he will run to succeed retiring Sen. Ben Nelson (D). The Nebraska seat is still a tough hold for Democrats, but Kerrey is the one recruit who can keep it in play for the party, which could, at the very least, force national Republicans to expend valuable resources.
On Wednesday, one day after Snowe's announcement, Republican strategists were noticeably unenthusiastic to discuss the Senate landscape and the increasingly complicated arithmetic needed for a majority. It was just the opposite for Democrats, some of whom said they could even foresee the party holding not only the majority, but its current 53-47 seat margin.
"At this point, you can make a reasonable case for no change and you can make a reasonable case for a Democratic gain," Democratic pollster Mark Mellman said. "Nobody thought that at the beginning of the cycle."
Democrats can negate potential losses in, say, Missouri and North Dakota by winning the two GOP-held states in New England ó Maine and Massachusetts ó which is hardly a long-shot at this point. Leaving off another potential Democratic pickup in Nevada, that means Republicans would still need to win four more Democratic seats; the most likely targets are Nebraska, Montana and Virginia, along with Wisconsin or New Mexico.
That is still doable, and the Republican target list remains long and even includes Hawaii. But the chips would continue to stack up against the GOP if Sen. Jon Kyl's (R) open seat in Arizona gets more competitive, which Democrats believe will happen when former Surgeon General Richard Carmona increases his name identification. He will have a tough race against Rep. Jeff Flake, who is expected to emerge from the GOP primary.