For starters, they helped conspiracy believers and even lunatics defeat what were generally more moderate, reasonable Republican candidates. In the hopes that those races would be a slam dunk if they could get the extremist as the opposing candidate.
It is already backfiring - and might have created the biggest threat to both the future of Democrats and the republic with the ascension of Kari Lake. She's like the perfect candidate - charisma, decades of media & message training, seems to understand the psychology of the mob. Instant frontrunner for Trump's running mate in '24, whether she wins or loses.
If Democrats lose some of those races now, they deserve it. It's not an honest way to treat competition. Neither party should try to meddle like that.