The gap between big media campaigns and canvassing operations favored by the grassroots can seem like a tactical Grand Canyon. But what if you could use advertising to draw a crowd of interested voters ripe for political conversations? And what if every one of those conversations were shared out to the participants’ friends as well as your candidate’s fans?

That’s Facebook Deep Canvassing, a new strategy we tested this spring with independent progressive Gayle McLaughlin in the California lieutenant governor’s race.

Early on in Facebook campaigning, developers and big vendors focused on making it easy for supporters to canvass friends and friends of friends on Facebook. But long before the Cambridge Analytica scandal, Facebook tightened its third-party integrations, effectively killing those efforts. Other consultants use Facebook like TV, billboards, mail, and other “dumb” media: aiming for mass impressions. Those are useful for seeding pre-canvass efforts, but fail to take full advantage of the platform that’s become central to American political discourse.

The deep canvassing effort we piloted depends first upon a huge number of post comments on a campaign’s page. For that, we created a large multi-variate campaign with hundreds of messages across our target audiences.

Using engagement-optimized ad spend, a standard Facebook campaign objective, we drove a high number of comments and shares — each of which pushes a personal endorsement of the candidate into a Facebook user’s feed.

Testing allowed us to consistently run ads with our candidate’s issue positions pinned on top of the trending stories of the day. This helped build momentum in real time instead of reacting to, say, poll results.

Each of those promoted posts generated a significant numbers of comments. In fact, several broke 1,000 responses. Moreover, we used ActionSprout to quickly filter our top performing posts by shares and comments.

Each positive comment became an open door for canvassing – both with official responses from the candidate page, and by trained volunteers who engage in open conversations. Because the comments are collected in easily sortable links to active posts, a volunteer canvasser can easily start 20-40 conversations per hour within targeted universes, from a group event or on their own time.

The advertising efficiency of Facebook Deep Canvassing is dramatic. While reach campaign Facebook ads function like billboards, mail, and TV – optimizing for impressions only – a successful engagement campaign garners additional organic reach as canvassers and new supporters continue to push your candidate’s content into more users’ Facebook feeds.

In our campaigns, we saw an 11 percent engagement rate with a 67 percent boost in additional free impressions over the paid. McLaughlin’s campaign quickly lapped all other candidates in her LG field with tens of thousands of interactions per week. Depending on the week, the McLaughlin engagement campaign had more reactions than the state’s most popular pols, including Gavin Newsom.

Facebook gave us an affordable advertising boost, created opportunities for volunteer canvassing, and revealed polling-like insights for improving the candidate’s email messaging, videos, and speeches.

Duplicating this strategy doesn’t require a California-sized advertising budget. We estimate that $500 per month is enough for a good start in most districts. We saw our pilot results at $500 a day — affordable for a serious statewide grassroots campaign and certainly an easier lift than California’s TV budgets that eat up hundreds of thousands per week.

Adriel Hampton is creative director at the Adriel Hampton Group, where he provides marketing strategy for progressive campaigns and technology companies. Shawn Kemp is co-founder of ActionSprout, where he has directly managed more than $3 million in Facebook ad campaigns for partners including CZI, 1,000 days, facebook.com/earth, Ashoka, and UNICEF.