One thing US Sen. Patty Murray (D-WA) is on the spot about these days is whether her party will maintain control of the US Senate; they're up narrowly, 51-47, after 2010 depleted the 60-vote advantage they had after Obama's big 2008 win.

And they're going to be on the defensive in 2012. I don't mean just because of the bad economy and low approval ratings for Congress: I mean because of the 31 seats up for reelection, 21 are currently held by Democrats. Oh, and today's big news puts good odds on one of those seats going to the GOP—conservative Democratic Sen. Ben Nelson (D-Nebraska) announced he's retiring.[pullquote]Republican voters keep trying other toppings, but then come back for the plain cheese.[/pullquote]

Most Democrats will probably cheer at first about the news; just this month, for example, Nelson sponsored legislation that could kill the health care reform law unless it includes even more restrictions on women's right to abortion. But ultimately, he did provide the 60th vote for health care reform, and he voted for Wall Street reform, two of the Democrats' big wins. And really, it's a numbers game: While Nelson's 79 percent average on voting with his party is low—most Democrats hover in the low 90s, including Murray and Sen. Maria Cantwell—having Nelson is certainly better for the Democrats than having a Republican in his seat.

As head of the Democratic Senatorial Campaign Committee, Murray spun the news for the Democrats today. Here she is in the New York Times:
In a statement calling Mr. Nelson “a loyal public servant,” Senator Patty Murray of Washington, the head of the Democratic Senatorial Campaign Committee, said she was optimistic about the Nebraska race and chamber as a whole.

“Republicans will continue to have their hands full with a very divisive primary in the state, which will provide an opportunity for Democrats to remain competitive,” she said. “We remain confident that we will hold the majority next year because incumbents have built strong campaign organizations in their states and we’ve recruited great candidates who are generating enthusiasm around the country.”

The Times gave the GOP the last word, though:
A spokesman with the National Republican Senatorial Committee took a different view.

“This retirement deals a real blow to the Democrats’ hopes of holding the majority and it’s an even deeper blow to their hopes of holding the Nebraska Senate seat,” said Brian Walsh, the communications director, in a statement.

Who's right? Well, in addition to the economy and the numbers, which both seem to be going against the Democrats, there are two other big factors: the two names at the top of the ticket.

Counteracting the bad news about Nelson is today's  Gallup Poll. Obama's approval rating is up; he's at 47-45. A Gallup poll taken right before Christmas that had him down 48-44.

As for the X-factor on the Republican side—it's looking more and more like Romney. Given his ability to excite Republicans so far—they keep trying other toppings, but then come back for the plain cheese—he's got some work to do if he wants to be a plus.

Oh, one other big factor: Money. Murray's DSCC has raised $38 million with $11 million on hand. The National Republican Senatorial Committee has raised $36 million with $9 million on hand.