As I noted in my New York Times piece this weekend,

Since 2005, I have tracked the rate of election litigation, which tells us how often plaintiffs go to court to fight over election rules. My latest research demonstrates that election litigation in the 2016 election season is up 23 percent over 2012. This follows a rapid increase of such litigation in the period after the disputed presidential election of 2000, when it more than doubled.

Here are a couple of graphic representations from my underlying study: