PORTLAND — It appears the decisive blow in the Portland mayoral election was delivered at a college party almost two decades ago.

On that evening, 20-year-old Jefferson Smith hit a young woman after she charged at him because she thought he shook or tipped a couch on which she was sleeping. Voters did not learn that information until October, shortly after it was disclosed that Smith has had his driver’s license suspended seven times.

Two polls released this week show the twin bombshells — and Smith’s heavily criticized response to the news reports — have probably cost him the election. Heading into summer, Smith was considered a slight favorite to defeat former City Commissioner Charlie Hales. Now he’s some 20 points behind in Tuesday’s race to replace Mayor Sam Adams, who declined to seek re-election after a scandal-marred first term.

Hales and Smith are Democrats and have similar takes on many issues, leaving Portlanders to contemplate factors such as character, style and likeability. After months of negative articles about both candidates, the polls suggest a significant number of voters might write in an alternate choice.

Smith’s reputation was already tarnished by his terrible driving record and a revelation that he was kicked out of a sports league for rough play. Then came the October disclosure, first reported by Willamette Week, that Smith was charged with misdemeanor assault after hitting an 18-year-old woman at a party near the University of Oregon in 1993. The charge was dropped when Smith did community service and paid the woman’s medical bills.

The damage escalated when the police report from the incident surfaced, portraying the young Smith in an unflattering light and partially contradicting the candidate’s memory of the event. Compounding matters, Smith paid an unannounced visit to the victim’s house after the news broke. Smith said he wanted to alert the woman that the story was being made public. He later realized the visit was a bad idea and apologized.

“I’ve been at this business for 36 years here, and I’m not sure I’ve ever seen a candidacy self-destruct like this,” said Tim Hibbitts, a prominent Portland pollster.

Hales had his share of negative press, starting with his acknowledgment that he lived in income tax-free Washington state for several years while continuing to vote in Oregon. He also got dinged for secretly recording an endorsement interview and submitting a letter to the editor that included passages lifted from The Oregonian newspaper.

Toward the end of the campaign, he broke a promise not to accept contributions of more than $600.

“I don’t think it would be unfair to say there’s not a lot of enthusiasm for either candidate, and I think Charlie Hales will basically win by default,” Hibbitts said.

Despite the downbeat press, the candidates have remained remarkably positive. Neither has exploited the other’s problems in television commercials and their debates have been civil.

Smith said his options in the difficult past few weeks ranged from quitting the race to going totally negative. He decided to keep running on the issues.

“We have to have the kind of politics that reflects that we are all in this together,” he said, “rather than the campaigns that say ‘everybody else sucks, vote for me.’”

Smith, 39, is a Harvard Law School graduate who had a brief legal career before starting The Bus Project, a nonprofit aimed at getting young people active in politics. He was elected to the state Legislature in 2008.

He seeks to boost education, improve the city’s core services and focus on outer East Portland, an unfashionable yet fast-growing part of the city in which most students receive free or reduced-priced lunches.

“It’s been tough, but life is tough and politics are tough,” he said of the campaign. “But what happened to me pales in comparison to the concentration of poverty that’s been developing in this town.”

Hales, 56, served as a city commissioner from 1993-2002. Under Portland’s commission form of government, the mayor and four commissioners share executive branch duties.

As commissioner, he pushed reforms that increased diversity in the fire department and was known for his support of parks, skateboarders, light-rail and the return of streetcars. He quit in the middle of his third term to join HDR Engineering as senior vice president, a job in which he promotes streetcars throughout the country.

Hales describes himself as a fix-it type who has the experience to get things done at City Hall. He said he will create jobs, fill potholes and change the culture of a police bureau that, according to the U.S. Department of Justice, has used excessive force too frequently.

“The real difference between Jefferson and me is not political ideology,” he said. “It’s action. I’ve proven the ability to make things happen.”

The one-time Republican has the reputation for shifting his positions; he doesn’t run away from the tag.

“The fact that I am willing to take in new information and change policy is, I think, a healthy thing,” he said. “Sure, some people will interpret that pejoratively — oh well.”