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Gordon Smith has conceded defeat.

(CNN) - Oregon Sen. Gordon Smith has conceded defeat to Democratic challenger Jeff Merkley in his re-election bid, CNN has confirmed.

Smith personally called Merkley earlier Thursday to concede the race, according to Merkley spokeswoman Julie Edwards. Smith is also expected to publicly admit defeat in a press conference later Thursday.

Election Center: Check out the results in Oregon

With 100 percent of the counties reporting, Merkley received 48.4 percent of the vote to Smith's 46 percent.

Smith's defeat means Democrats now hold 57 seats in the Senate. The outcomes of three races remain unclear - Alaska, Minnesota, and Georgia.

A new ad from Gordon Smith’s campaign stresses his work with Barack Obama.

(CNN) - Republican campaigns have launched a slew of ads this year looking to tie Democratic congressional candidates to Barack Obama. Now the Illinois senator’s name is making another appearance in a new GOP spot this week - the second ad from Oregon Senator Gordon Smith that stresses his own working relationship with the presumptive Democratic nominee, and with Massachusetts Senator John Kerry.

"Times are tough. Rising prices on gas, food, health care. Families need help. That's why I choose to reach across the aisle,” says Smith in the new spot. “With John Kerry to protect homeowners from foreclosure, with Barack Obama for better gas mileage. And when President Bush tried to cut Medicaid, the Oregon health plan, I said no. What matters is helping people, not who gets the credit.”

Last month, Smith plugged his work with the Illinois Democrat to push for stricter mileage standards for automobiles.

Smith may be highlighting his ties to Obama - but he can’t boast a nod from his Senate colleague, who supports Democratic opponent Jeff Merkley.

Smith is hoping to benefit from Obama in a new ad.

(CNN) - Barack Obama's name is likely to help several Democratic candidates down ballot, but what about a Republican?

Oregon Sen. Gordon Smith, one of the most vulnerable Senate Republicans, is stressing his history of working with the presumptive Democratic nominee in a new campaign ad hitting airwaves Tuesday.

"Who said Gordon Smith helped lead the fight for better gas mileage and a cleaner environment? Barack Obama," the ad's narrator states. "He joined with Gordon and broke through a 20 year deadlock to pass new laws which increased gas mileage for automobiles."

The Obama campaign immediately made clear the Illinois senator is supporting Smith's Democratic opponent.

“Barack Obama has a long record of bipartisan accomplishment and we appreciate that it is respected by his Democratic and Republican colleagues in the Senate," Obama spokesman Bill Burton said. "But in this race, Oregonians should know that Barack Obama supports Jeff Merkley for Senate. Merkley will help Obama bring about the fundamental change we need in Washington."