PORTLAND, Ore. (AP) – Clerks slogged through a mountain of ballots Oregonians turned in at the last minute, but the outcome of the U.S. Senate race between challenger Jeff Merkley and incumbent Gordon Smith remains too close to call. Late Wednesday, only about three-fourths of the expected vote had been counted and the two candidates had swapped narrow leads. That raised the possibility the outcome of one of the nation’s most-watched Senate races might not be known until Thursday.