Washington (CNN) A trio of Democratic groups are wading into the upcoming Ohio 12th Congressional District special election with a joint advertising and field campaign, part of a rush of Democratic engagement in the last two weeks of a contest that will serve as a key test ahead of the 2018 midterms.

The three groups -- House Majority PAC, Priorities USA Action and For Our Future -- announced Wednesday the launch of a "joint $140,000 investment in a digital and field campaign" aimed at bolstering Democrat Danny O'Connor against Republican state Sen. Troy Balderson in the race for former Republican Rep. Pat Tiberi's seat.

The organizations say the initiative will run through Election Day on August 7, with Priorities USA helming the digital ad campaign and For Our Future leading canvassing and get-out-the-vote efforts.

"Troy Balderson supported a massive tax giveaway to corporate special interests -- and you pay for it," a narrator says in the spot before listing concerns about the national debt, welfare programs and the possibility of higher future taxes. "It's simple: Troy Balderson will cost you more."

The ads will run on Facebook, Pandora, Spotify, YouTube and Google. The groups plan to combine advertising and going door to door, with the goal of knocking on 25,000 doors.

House Majority PAC director Charlie Kelly hailed the joint initiative in a statement: "House Majority PAC is proud to partner with Priorities USA Action and For Our Future -- investing both in field and a range of new media platforms to go on offense in this red district. From front doors to digital platforms, we're going to make sure voters know Balderson sure doesn't stand with them on the critical kitchen table issues defining this election and would cost them more."

The new campaign tracks with escalating Democratic activity in the 12th District special election, a race that's been dominated by Republican money for months. Outside groups have spent over $4 million on the race, most of it coming from GOP organizations, due in part to a competitive primary on the Republican side. The Congressional Leadership Fund, a leading GOP super PAC targeting US House races, has spent nearly $2 million on the race alone, according to Federal Election Commission filings.

Democrats are banking that the enthusiasm of their base this election cycle, coupled with effective messaging against President Donald Trump's economic policies, will be enough to flip the district that Tiberi, who left office earlier this year to lead the Ohio Business Roundtable, had represented since 2001.

Last week, the Democratic Congressional Campaign Committee -- House Democrats' principal campaign arm -- dropped $238,000 on a 10-day ad campaign running through next Monday. And the expectation is that the committee will buy more airtime to run pro-O'Connor spots through Election Day.

Like the video featured in the new campaign from the Democratic groups, the committee's ad targets Republicans' tax plan

"Balderson supports a massive corporate tax break that helps rack up $2 trillion in debt. And what will that mean for us? Balderson's plan could mean cuts for Medicare and Social Security," warns a narrator in the Democratic Congressional Campaign Committee spot.

Josh Schwerin, communications director for Priorities USA Action -- one of the three groups involved in the new campaign -- spoke to Democrats' confidence in attacking the GOP tax cuts in the midterm elections, a tack that's been a big part of the party's messaging in the Ohio special election.

"Republicans promised thousands of dollars to every American family and a political silver bullet. The actual result has been lower wages and a ballooning deficit that Republicans want to use as an excuse to cut Medicare and Social Security. There isn't a district in America where we'd be remotely worried about running ads highlighting the damage the Republican tax law is doing to the country," Schwerin told CNN.

An O'Connor win in this pink district would be a shot in the arm for Democrats concerned about the party's recent losses in the industrial Midwest, epitomized by Trump's 2016 victory in Ohio. The recent commitment of resources to the 12th District special election suggests the party thinks it has a real shot.