Yesterday, Maine Senator Olympia Snowe announced that she would not seek re-election in November. Her rationale for doing this, according to a Washington Post report, was that it was almost impossible to accomplish anything there because of political partisanship. She added, “Unfortunately, I do not realistically expect the partisanship of recent years in the Senate to change over the short term. So at this stage of my tenure in public service, I have concluded that I am not prepared to commit myself to an additional six years in the Senate.”

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She was regarded throughout her tenure in the Senate as a voice for compromise. She was one of the leading members of the “Gang of 14”, a group of senators from both parties which was formed to prevent the filibuster of judges. Many in this group were targeted by activists in both parties; with her gone, I believe there are only five left in the Senate.

What does her departure mean? Well, in political terms, it makes it much more difficult for the Republicans to take control of the Senate. Assuming Obama wins the Presidential election in November, the Republicans would need to gain 4 seats to achieve control. With Snowe’s departure, the favorite to win her seat is a Democrat, Representative Chellie Pingree, who lost when she ran against Susan Collins, but has maintained high name recognition in the state. As well, the news that Bob Kerrey will seek the Nebraska seat that Ben Nelson is leaving makes that race competitive.

Snowe’s claim that partisanship has climbed recently is common knowledge to political scientists. There are a number of reasons for this. One explanation is that the Democrats, which used to be centered in the Rust Belt, have become more dependent on the Northeast and the West coast states, which are more liberal. Likewise, the Republicans used to be dominated by the farm states, but their base has steadily moved to the Gulf States and those adjacent to it, which are more conservative. Many political scientists expect this trend to be mitigated in 2014 or 2016 when Texas will become a purple state.

Snowe’s decision was not revealed to others in her party until a few hours before she made it. It is thought that her decision was driven by the Blunt Amendment, which is scheduled to be voted on today. She appeared on MSNBC soon after the retirement announcement, where she stated, “It’s much broader than I could support. I think we should focus on the issue of contraceptives and whether or not it should be included in a health insurance plan, and what requirements there should be.” She presumably would have had a lot of pressure to support the bill, since she expected to face a challenger in the Republican primary.