Which IndyCar race will be dropped in 2017?

When talking about the 2017 IndyCar schedule, IndyCar CEO Mark Miles said to racer.com, "….we're good with everyone on this year's calendar except one, so there's not a whole lot of room [for new races]."

Which 2016 race is Mark Miles suggesting might be dropped? Texas attendance has been dropping precipitously. Sonoma attendance is always marginal. Iowa attendance has been dropping now that NASCAR owns the track. Any other guesses?