After Citizens United, the government has a much harder time regulating campaign donations, but it can still tax them, right? How about a progressive tax on donations to candidates, political parties, and 527 groups? The first $1000 could be tax-free, and then the tax would gradually rise to 100% once you donate up to, say, $5000 to any given group. Such a tax would have brought in billions in this last tax cycle or, even better, reduced the amount of money spent by the campaigns.
The tax revenue could be dedicated to bolstering democracy: public finance of campaigns, ensuring adequate voting technology in every district, non-partisan voter information campaigns like the old League of Women Voters pamphlets.
I know, the Republican House would never go for it. But public opinion is very strong against money in elections, so it might at least be worth a try.