Control of the US Senate is at play in the 2014 election, which means tight races and tremendous spending from outside groups. Outside spending in the top nine Senate races in 2014 is almost equal to spending in all 37 races in 2010. Half of the independent spending in the top nine races comes from dark money groups, that do not fully disclose the source of their funding.
The Brennan Center provided an analysis of outside spending in the most competivive Senate races, which observed "inadequate transparency and single-candidate spenders providing opportunities to avoid contribution limits." To review the full analysis, click here.