(Bloomberg) — Democrats are exploring a new attack line against the Koch brothers and Republican allies, telling voters the billionaire energy executives want to let home flood insurance premiums soar to help corporate America.

It's a potentially potent message in coastal states such as Louisiana, Georgia and North Carolina, where U.S. Senate elections in November are critical in the fight for control of the chamber. The flood insurance debate also has surfaced in Mississippi, where it may harm a Senate candidate aligned with the limited-government Tea Party movement who is pursuing a primary challenge against a Republican incumbent.

The issue's emergence follows congressional votes last month that averted steep premium increases in the more than $3 billion annual flood insurance market. The legislative action angered some in the Tea Party movement, who say those living near water should bear the risk, not taxpayers now responsible for $24 billion in flood insurance debt.