It's Election Day today, in the special election for Sen. Kirsten Gillibrand's former House seat in upstate New York. Democratic candidate Scott Murphy may be the slight favorite -- a recent Siena poll gave him a four-point lead -- in a campaign that many outside observers originally thought could be a likely pick-up for the GOP. No matter which way it turns out -- we'll find out after the polls close at 9 p.m. ET -- expect it to be close.

Republican candidate Jim Tedisco, the state House minority leader, began this race two months ago with high name recognition, while Murphy was an unknown businessman making his first bid for office -- indeed, a Siena poll from a month ago put Tedisco ahead by 12 points. Both national parties have been actively involved with the race, with the NRCC spending over $800,000 and the DCCC putting in about $590,000 -- plus $820,000 from the National Republican Trust PAC for Tedisco, and $245,000 on Murphy's behalf from the SEIU Local 1199. Murphy himself has out-raised Tedisco's campaign, and in all the money spent is about even on each side, totaling roughly $5 million.

Among Democrats, the mood is generally one of cautious optimism, while Republicans are uncertain -- and of course, both sides are staying focused on their ground game. The bottom line here is that it's impossible to fully predict turnout in a special election -- it must be earned, vote by vote.

At first glance, it seems hard to believe that Democrats had this district at all -- but there is an explanation. According to the most up-to-date registration statistics, provided to TPM by the state elections board, the district is 41% Republican to only 27% Democratic. And yet Kirsten Gillibrand picked it up in 2006 and was easily re-elected in 2008, and Barack Obama narrowly carried it in 2008.

So in practice, the unaffiliated voters have really become soft Democrats by a wide margin, more than making up the difference -- meaning that this is a Republican district on paper only, and a genuine toss-up in the real world. The question for Dems is whether they can hold on to these newly Dem-leaning independents, and also turn them out to the polls in a special election.

And Democrats have found their winning issue -- namely, Murphy has built his own brand by tying himself to the very popular President Obama, and support for the stimulus package, at just about every step of the race. Obama has endorsed Murphy via e-mail, and Vice President Biden has now done a radio ad for him. On top of that, Murphy's campaign literature makes an easy-to-understand pitch to voters: You can help Obama by voting for Murphy.

Tedisco, meanwhile, has run a populist campaign, and has accused Murphy of supporting the AIG bonuses, by virtue of Murphy's support for the stimulus bill and the curb on executive pay that was explicitly made not retroactive. It's an unusual development, with the Republican attacking the Democrat as an out-of-touch businessman -- and an important test case of whether this line of attack from the GOP can stick down the road, versus Obama's current personal popularity.

Fun fact: Murphy already starts out with a one-vote lead, having gone to the polls this morning. Tedisco, however, can't actually vote for himself because he doesn't live in the district. A portion of Tedisco's state legislative seat is within the House district, but not the part where he actually lives. It might only be one vote, but hey -- special elections do have low turnout.