Obama and gay marriage comes to mind..i knew he was lying, but hes a good BSer and people fell for it...
Dems can lie because they do it with a wink to the base. Their base knows they're lying to get elected and doesn't force them to publicly pledge supporting unpopular positions.
If a Republican ran on anything other than a total ban on abortion, half the people on the site would be screaming, "RINO! BABY KILLER! YOU'LL NEVER GET MY VOTE!"
So Republicans have learned they need to bend the knee and kiss the rings of the single-issue voters in the base and then somehow figure out how to pivot to the center in the general campaign.
Democrats don't have this problem. Their base is smart enough to allow their candidates to keep their mouths shut and campaign as a moderate until the moment the polling places close.