A Florida-based super PAC that made more than $1 million in contributions in 2010, almost all of it underwritten by the former CEO of online brokerage TD Ameritrade, is emerging as a factor in Tuesday's Republican Senate primary in Nebraska.

In the three days before the election, the Ending Spending Action Fund has dumped almost $255,000 into the race to help Deb Fischer, a state senator who has suddenly turned an already-heated contest for the GOP Senate nomination into a three-way race. The group has not yet disclosed any donors this year, but in the 2010 campaign cycle ...