Democrats are favored to hold Oregon’s 1st district in today’s special election, which marks the first Congressional contest of 2012.

State Sen. Suzanne Bonamici (D) and businessman Rob Cornilles (R) should know by tonight which one will represent the district through the end of the year. Ballots, distributed two weeks ago, must be returned by 11 p.m. EST in the all-mail election to fill the seat left vacant by the resignation of former Rep. David Wu (D) in August.

Democrats spent big to hold this Portland-area seat, which the party has controlled for the past four decades and President Barack Obama won with 61 percent in 2008. Needing to pick up 25 seats to regain the House majority and hoping for some momentum, the party could not risk starting the year with a loss in a comfortably Democratic district.

“There is a narrative here that this is really the beginning of the 2012 elections,” Oregon Democratic Party Executive Director Trent Lutz said. “This is the first special of the year, so in some shape or form, it is something to pay attention to.”

The Democratic Congressional Campaign Committee invested $1.3 million in the race, mostly on TV ads that portrayed Cornilles as a tea-party-affiliated Republican — not the moderate he painted himself to be on the campaign trail.

The DCCC was not alone, with the Democratic-aligned House Majority PAC investing $300,000 on ads and direct mail and EMILY’s List spending $200,000, all to help Bonamici win a district few political observers believed at the start was competitive. Public polling showed Bonamici with a solid lead, but the Cornilles campaign released a poll this month that had him down just 4 points.

If Bonamici wins, as expected, it would be the first of three House vacancies created by scandal this cycle that was retained by the party that previously held the seat. Both parties lost a seat with the resignations of New York Reps. Chris Lee (R) and Anthony Weiner (D) in 2011.

In the two other previous special elections, Democrats held the seat  of former Rep. Jane Harman (Calif.) and Republicans held the seat of now-Sen. Dean Heller (Nev.). There is at least one more special to go, as Democrats try to hold the seat of former Rep. Gabrielle Giffords (Ariz.).

“We never take any race for granted,” DCCC spokesman Jesse Ferguson said. “The DCCC made smart, strategic investments in a race where voters aren’t used to special elections to prevent the Republican candidate from hiding his extreme tea party roots and dangerous views on Medicare.”

The National Republican Congressional Committee, which contributed $85,000 to Cornilles for a coordinated ad campaign, is painting the race as a “money pit” for Democrats.

“If they are spending more than $1 million to try to retain a seat in a district that Barack Obama won with nearly 62 percent of the vote, Democrats face a devastating reality this November in districts where their candidates are frantically trying to hide their ties to Obama’s corrosive policies,” NRCC spokesman Daniel Scarpinato said.

Both campaigns prepared for robust get-out-the-vote efforts over the weekend and on Monday, as all-mail elections usually receive a spike in ballots in the final two days. The most votes will come from suburban Washington County, where county elections officials expected to receive 30 percent of all their ballots on Monday and today.

Asked how the campaign was feeling heading into the final weekend, Bonamici consultant Mark Wiener would not share the campaign’s internal polling, but he pointed to both campaigns’ last TV ads as an indication of how each viewed its candidate’s standing.

Bonamici issued a positive spot for her final salvo that quoted several local newspaper endorsements, including from the Portland Oregonian. Cornilles’ ad tied Bonamici to Wu, who resigned following a sexual assault allegation.

“They’re doing this desperate Hail Mary pass that nobody believes is going to have any impact, and we’re able to finish out strong and positive with the basic message of why Suzanne wants to be in Congress,” Wiener said. “That’s probably pretty telltale right there.”

The Cornilles campaign, cognizant it needs crossover voters to win, hopes the onslaught of Democratic ads has the opposite effect for Bonamici, turning off Democratic voters and pushing them to either vote for Cornilles or not at all.

“We’ve always felt that for Rob to win this thing he’d need a surge at the end,” Cornilles campaign manager Mary Anne Ostrom said. “And there’s no reason to believe that the momentum that started a few days ago isn’t continuing.”