You're assuming they care about keeping their corruption hidden. They want absolute power! Who cares if the people know the system is corrupt if there's nothing they can do about it. Most dems are already aware that this is a fight for democracy itself, and the reps will just say they're "using the corruption to their advantage so they can fix it" or something.
The strategy you've outlined relies too heavily on their winning the election fairly. Don't get me wrong, it's not impossible, but it's far from a sure bet.