New polling showing Democrats defending their U.S. Senate seats in battleground states taking commanding leads is evidence that Vice President Kamala Harris presidential bid has been a boon for her party. That is the opinion of Democratic pollster Fernand Amandi, who appeared on MSNBC’s “Morning Joe” on Thursday to explain the impact Harris has had in the few weeks since she replaced President Joe Biden at the top of the 2024 ticket. After sharing polling data from the Cook Political Report showing Senate Democrats in Arizona, Michigan, Nevada, Pennsylvania, and Wisconsin seeing their leads ju…