BERLIN, Aug 7 (Reuters) - Germany"s Social Democrats have broken a taboo in modern German politics by taking aim at the religious beliefs of a close aide to Armin Laschet, the conservative candidate to succeed Chancellor Angela Merkel after a Sept. 26 election. In a video published online, the left-leaning Social Democratic Party (SPD) singled out a number of leading conservatives including Nathanael Liminski, who heads Laschet"s office in his regional government in North Rhine-Westphalia. Liminski, a practicing Roman Catholic, gained attention as the voice of Generation Benedict, a church group he co-founded following World Youth Day 2005, which supported the positions of Pope Benedict XVI. "Whoever votes for Armin Laschet and the CDU, votes for ... ultra-Catholic Laschet confidants for whom sex before marriage is a taboo," the narrator says as the video shows a Russian doll bearing Liminski"s face, inside a bigger doll bearing Laschet"s face. By highlighting a rival"s religious beliefs, the SPD is breaking with a tradition in consensus-oriented Germany of avoiding personal attacks in election campaigns, especially on matters of faith. "The political debate is becoming ever more divided by cultural issues," said Carsten Nickel at Teneo, a political risk consultancy. "The SPD is trying to wake up this campaign by mobilising supporters around cultural questions." In the video, the SPD took aim at other leading conservatives, arguing that supporting them would make the rich richer and the poor poorer, and push the party to the right. The conservatives promise voters "stability and renewal" in their manifesto. read more The video, streamed live on Wednesday, ran at the end of a half-hour presentation by SPD General Secretary Lars Klingbeil. An SPD spokesperson, contacted by Reuters, said it was a "social media clip" and was not an election campaign commercial. Leaping on the video, the Tagesspiegel newspaper ran a headline on Saturday reading: "Laschet targeted by "negative campaigning": The SPD breaks a taboo in the election campaign". Ahead of September"s federal election, the party is trying to convert the popularity of its chancellor candidate, Olaf Scholz, into support for the wider party. An opinion poll published on Thursday showed that in a hypothetical direct vote for chancellor, Scholz would be the most popular candidate to lead the next government. Laschet bled support after he was seen laughing on a visit to a flood-stricken town. However, Laschet"s CDU/CSU alliance still leads other parties. Merkel, in power since 2005, plans to stand down after the election.