Wonder will headline a fundraiser for Landrieu as she seeks to move past Keystone vote.
Republicans hope Gov. Brian Sandoval challenges the soon-to-be Senate minority leader.
But the Louisiana Democrat argued the bill's failure won't undermine her reelection efforts.
Some proceeds from the Dec. 1 event will go to Cassidy ahead of his runoff election.
The GOP might have trouble replicating its success in two years.
The Kentucky Republican is expected to run for both the Senate and presidency.
The GOP is likely to have a 54-seat Senate majority next Congress.
The gun rights group's new ad ties the Louisiana Democrat to President Obama.
Laura Barron-Lopez 11/17/14 08:10 AM EST
The senator, who's facing a tough runoff, pushed for a vote in the Senate.