Political parties are using increasingly meticulous screening practices to stop damaging revelations about candidates from surfacing during the upcoming federal election campaign — everything from scouring social media sites to conducting criminal and bankruptcy checks.

The major parties have tasked teams with carefully scrutinizing each nominee to uncover any racist or homophobic remarks, or any other instances of inappropriate behaviour, that could embarrass or derail a campaign.

For the Green Party, growing support in the polls has meant more nominees vying to become candidates — and an even greater need to vet them thoroughly.

Green campaign manager Jonathan Dickie said every nominee is asked to proactively disclose anything from their past which could be "problematic" for the party. A team of vetters then scans candidates' background and digs deeper if it finds red flags.

More than 20 nominees have been disqualified from running for the Green Party because of past behaviour or values that don't match up with the party's principles.

"It's a small percentage of the overall, but definitely there's been a few we just can't move ahead with," Dickie said.

"Usually it's social media posts, where it just leads us to believe that this would not be a good candidate, that they would cause some damage to our reputation, or that their positions just don't align with our positions. And through a subsequent conversation, we just realize they're completely incompatible."

As part of the NDP's vetting process, nominees are required to sign a confidential disclosure form attesting they share the party's political values, including its approach to women's and LGBT rights. Internal party vetters review the form and the contestant's social media footprint.

But doing due diligence can come at a cost. At least one prospective NDP candidate, longtime union activist Sid Ryan, dropped his bid for the Oshawa nomination last month, citing a sluggish process that wouldn't leave him enough time to run a proper campaign.

Weaponizing a politician's past

Deep dives into candidates' records can serve a campaign in two ways: by heading off scandals before they erupt, and by digging up damaging material to use against opponents.

NDP strategist Kathleen Monk said deploying a candidate's indiscretions can knock a party off-message at critical points in the campaign and force a party leader to spend precious campaign time defending a candidate's past actions. Social media sleuthing is a key tactic used by partisan researchers to put opponents on the defensive.

"You try to unearth the more unsavoury parts of their background — beliefs, for instance, that would be abhorrent," Monk said.

"We then, within the electoral period, will raise those issues and ask leaders if they stand by their candidates who hold said beliefs. In doing so, the objective is to weaken the opposing party by having the leader either have to ditch their candidate or have to stand by an unsavoury character."

Discrediting candidates, maximizing damage

The practice of digging up dirt on political opponents is as old as democracy itself, but Facebook, Twitter and other social media sites can offer scandal-seeking party operatives a potential gold mine of past missteps. Parties tend to sit on such material, waiting for the right time to deploy it to maximize the political damage.

The ultimate goal is to knock a candidate off the ballot.

New Liberal national nomination rules require that an Electoral District Association (EDA) conduct a thorough search for women candidates and other candidates who reflect the demographics of the community before a nomination can proceed.

The Liberal Party of Canada says its "Greenlight Committee" scrutinizes each prospective candidate to ensure a clean slate and its rules stipulate that candidates must not have "engaged in any claim, litigation or dispute of any sort which is liable to bring controversy or disrepute upon the qualified nomination contestant or the Party."

"Canadians expect all parties to do their due diligence on all prospective candidates, and as in 2015, the Liberal Party of Canada is following a rigorous green light process for candidates in this fall's important election," said Liberal Party spokesman Braeden Caley in an email.

The Liberal Party already has ditched one candidate — Hassan Guillet — over past comments that were deemed anti-Semitic.

The Conservative Party was the first to nominate a full slate of 338 candidates. Each one was required to sign a 50-page questionnaire and was scrutinized by a team of vetters.

Jerry Bance was removed as a Conservative candidate in the 2015 election after video surfaced showing him urinating in a mug while working as a service technician. (Conservative.ca/CBC)

The party is likely working hard to avoid a repeat of a 2015 fiasco, when video surfaced showing a technician caught on hidden camera urinating into a coffee mug during a 2012 house call to repair a leaky sink. He later became a Conservative election candidate.

He was removed from the roster.

CPC spokesman Cory Hann said the comprehensive vetting process weeded out several candidates this time. Many of them are now running for the People's Party of Canada (PPC) after losing nominations or being rejected by the Conservatives, he said.

PPC executive director Johanne Mennie said the party does have a candidate vetting process but its details are confidential because it is an internal party matter.

Daniel Beland, a political science professor at McGill University, said the explosion of social media platforms has spawned a growing source of electoral danger for political parties.

Candidate vetting is more challenging than ever, he said, because people don't always remember what they posted on Facebook or Twitter five or 10 years ago — and even when they do know, they might not divulge it to their party.

"Parties are always waiting for candidates from other parties to make mistakes, or to exploit negative information about their past statements or activities, in real life or on social media," he said.

"Negative stories about your candidates are free ammunition for the other parties and their supporters, who will use social media to amplify negative stories about their opponents."