Bonamici's campaign has placed a series of airtime buys in Portland for the four weeks left until the Jan. 31 election, totaling about $100,000, according to Smart Media Group.

Bonamici campaign manager Carol Butler, in a statement announcing the ad, accused Cornilles of being "the first candidate of the special election to go negative on television." That may technically be true — Bonamici's previous spots have been positive ads touting her work as a consumer protection attorney and a state lawmaker — but Cornilles certainly hasn't been alone in going negative.

The Democratic Congressional Campaign Committee, EMILY's List and Planned Parenthood have attacked Cornilles with ads designed to boost Bonamici's candidacy. But thee groups by law cannot coordinate with her campaign.

All told, Democratic and liberal groups have spent close to $1.5 million on Oregon's airwaves to undercut Cornilles.

Like Bonamici, Cornilles used his first ads of the campaign to introduce himself to voters — although noticeably absent were any references to his Republican affiliation in a district that leans heavily Democratic.

But on Tuesday, Cornilles put out an attack ad of his own, reportedly dropping $100,000 to juxtapose his private-sector experience with Bonamici's career as a liberal state lawmaker.

"Incredibly, Bonamici can't recall ever voting against a tax increase or fee hike, and she has no record of job creation," the Republican's ad states.

The election to replace Wu, who resigned in June amid a sex scandal, is being conducted entirely through mail-in ballots. Although special elections always attract outsize amounts of attention as both parties look for signs of their electoral fate in other races, the Oregon race has been somewhat upstaged by the chaotic race for the Republican presidential nomination.

Watch the ad: