Political advertising is taking over television airwaves in battleground states, but complementary online advertising is also ubiquitous and being used by campaigns more than ever before.

Presidential campaigns, especially President Barack Obama’s, have been at the forefront of digital political advertising. But this cycle, Congressional campaigns are catching up, using their Internet pitches not only as a fundraising tool, but as a key component of their strategy to target voting blocs.

There are “substantially more campaigns at the House and Senate level than last cycle, but it’s not just that they’re using it, it’s how they’re using it,” said Rob Saliterman, head of GOP advertising outreach at Google and former spokesman for President George W. Bush.

Television remains the dominant medium for campaign communication.

But digital strategy firms from both parties are working with campaigns at all levels – from the presidential to provincial – to capitalize on the targeting opportunities that online advertising provides. They are adapting new technologies and putting an increased emphasis on the digital as the media marketplace continues to fragment.

The number of people watching videos online is skyrocketing, according to digital data compiled by comScore. It reported on Tuesday that an all-time high of 188 million internet users in the United States watched 37.7 billion online videos in August, with 9.5 billion video ads viewed.

Thanks to techniques such as voter-file online ad targeting – which emerged late in the 2010 cycle – it’s easier than ever for campaigns to show their ads to only the groups of voters they are targeting.

Pre-roll video – where a 15- or 30-second ad airs before the video the viewer wanted to watch starts – was rarely used by political campaigns before the 2010 cycle. Since then, both the use of pre-roll video ads and the amount of available advertising space – known as “inventory” – in which to air such ads have increased dramatically.

“This is a consequence of a couple of different things going on in the changing media landscape,” said Eli Kaplan, a Democratic digital strategist at Rising Tide Interactive. “More and more people are watching video online, and more and more publishers are seeking to monetize that inventory by putting pre-roll video advertisements in front of it.”

That’s led companies including AOL, Google, Facebook and Twitter to hire strategists from the political world to help with outreach to potential advertisers. Just on the Republican side, along with Saliterman joining Google, Twitter hired GOP digital strategist Mindy Finn; Facebook brought on Katie Harbath, the former chief digital strategist at the National Republican Senatorial Committee; and AOL snapped up John Randall, the former e-campaign director at the National Republican Congressional Committee.

“There’s two sides to the story,” said Peter Pasi, a Republican digital strategist and executive vice president at Emotive. “Are campaigns reaching out more, are they really recognizing the value of online advertising? Or are the companies that sell advertising reaching out more? I think it’s both.”

According to Saliterman, campaigns can now specify when advertising with Google that their pre-roll ads only be shown to viewers in a particular Congressional district. And the targeting possibilities dive deeper than that, especially with the advent of voter-file online ad targeting.

Campaign Grid, a Republican advertising platform, was the first to use the technology in the political sphere late last cycle. Essentially, the technique matches voter file data with Internet records. Registered voter data can be matched with web users if they, say, offer their name and address when making a purchase.

After the data is matched, it’s anonymized by a third party to avoid any breach of privacy, and the user is simply non-personal identifiable data points. Those data points – such as whether they’re a likely voter, their party affiliation and age range – allows the voters to be added to “buckets.” Campaigns wanting to reach particular types of voter can then choose to display their ad only to the selected buckets of voters.

“We’re targeting the same way consultants have been targeting people with phones and mail for decades,” said Jordan Lieberman, president of Campaign Grid.

Jim Walsh, CEO of DSPolitical, an advertising firm on the Democratic side, said major private-sector advertisers have been using this technology for years to reach specific audience segments they deem likely customers.

“They just call it ‘audience targeting,'” he said. “Almost immediately, we realized the electoral applications if political data could be matched to these online audiences. So we adopted this same technology and tailored it specifically for the political space.”

With an increased ability to target, campaigns are seeing new avenues of persuasion online, not simply a mechanism for raising money like Obama’s campaign did so successfully in 2008. Digital strategists would argue that, with DVR, smartphones and tablet use on the rise, a significant portion of the electorate is completely missing candidates’ messages on TV.

A study released by SAY Media last month, “Voters Going off the Grid: 2012,” found that voters are increasingly watching less live TV. The bipartisan study, conducted in partnership with the firms Targeted Victory, Public Opinion Strategies, Chong & Koster and SEA Polling, found that 29 percent of likely voters had not watched live TV in the past week.

“The game-changer this cycle is that online is a persuasion vehicle,” said Michael Beach, co-founder of Republican digital strategy firm Targeted Victory. “I think that will be second nature to people next cycle.”