Online video ads have become a serious outreach avenue for political candidates, and especially President Obama and Mitt Romney in the 2012 Presidential campaigns. TV inventory is hard to come by at this time of year, so the campaigns – and the Super PACs that surround them – have been embracing the online channels. For the businesses on the other side of the equation, that means an important new source of revenue.

Multi-screen video ad company YuMe, which provides software for brands and publishers, has seen an evolution in online political advertising since the last election cycle. In 2008 and 2010, campaigns treated online video as an after-thought, mostly just repurposing their TV content for the online medium, says Ed Haslam, YuMe’s senior vice-president of marketing. At that point, digital video ads were experimental, he says. Now, however, the campaigns are much savvier. “Digital planning and digital strategy at the master campaign level is a lot more coordinated, a lot more well thought out,” says Haslam.

Citizens United,” a Supreme Court ruling that gave the green light to “independent” campaign donations and led to the formation of SuperPACs, has been a key driver of the new influx of money and focus on digital platforms. Hurtful to democracy? Maybe. Good for the bank accounts of ad:tech companies? For sure.

“The influx of money makes the market segment more interesting to us,” says Haslam, in a display of cautious understatement. Would companies in the online ad space be doing as well this election cycle if “Citizens United” had never passed? “I don’t think it would have been as big, no,” says Haslam. “Without a doubt.”

Online video ads have increased awareness related to candidates, earned more influence, and become a new fundraising avenue, Haslam says. The segment has grown to a point where politics is now competitive with auto and entertainment among YuMe’s major money-earners. “We’re now treating it like any other category.” Online spending in the 2012 elections is expected to hit $160 million, according to Borrell Associates. That figure is six times higher than the 2008 elections.

Since the debates, YuMe says interest in online video ads has intensified. Following the debates, video ad campaigns have performed twice as effectively in terms of interaction rates and 15 percent better for completion rates (as in, the rate of people watching the videos to the end). For example, completion rates on October 4, the day after the first presidential debate, hit 78 percent, a full 11 percent higher than the average for other days in October.

Viewers have also been paying closer attention to online video ads as election day approaches, which is hardly surprising. In October, interaction rates hit 1.3 percent (including the post-debate spike), compared to 0.68 percent in July, 0.88 percent in August, and 0.9 percent in August. Video completion rates also rose steadily, from 59 percent in July to 71 percent this month.

Voters have indicated that they don’t actually hate online ads that much and even prefer the targeted nature of online advertising to the alternatives, according to online research firm Toluna. In a recently released survey of more than 1,000 people, Toluna found that while 60 percent of respondents view political advertising as a “bad thing,” close to the same percentage said that improved targeting was a “good thing,” according to AdAge.  Respondents aged between 18–34 years old responded most positively, with 65 percent of the sample saying they can put up with companies gathering information on their online habits if it results in better targeting.

So what online ads are working well for the candidates? Well, this week, Obama has enjoyed the support of celebrities from Jay-Z (pictured above) to Rosie Perez, and Romney has taken his opponent to task for sounding a lot like he did in the last time round. Here are the five most viral political ads of the week, according to the Wall Street Journal (which gets the info from Visible Measures).