 A growing number of other top Democrats have asked the president to step aside. Tester's past support for Biden has been the focus of Republican attack ads against him. Tell John Tester, stop standing up for Joe Biden and start fighting for Montana. Tester faces Republican challenger and former Navy SEAL Tim Sheehy. The Cook Political Report says the race is a toss-up. It could decide the balance of the U.S. Senate. For NPR News, I'm Shaley Riker in Helena.