Nate Cohn, writing in...

...the New Republic, argues that the NRA may not be as powerful as everyone thinks (my emphasis):

But real senators with low NRA ratings routinely win Senate elections in culturally conservative states. Bill Nelson has an "F" from the NRA and campaigned on gun control in 2000, yet he always outperforms Democratic presidential candidates in culturally conservative stretches of northern and central Florida. Nelson isn’t the only Democrat succeeding in Dixie with an “F.” He’s joined by Senators Tim Kaine ("F"), Kay Hagan ("F"), Jay Rockefeller ("D"), and Claire McCaskill ("F"). In Ohio, where John Kerry went hunting before the 2004 presidential election, F-rated Sherrod Brown carried much of the southeastern part of the state in 2006 and cleanly won a second term in 2012. Senator Heidi Heitkamp could have peered across North Dakota’s eastern border and noticed F-rated Amy Klobuchar winning rural, conservative, western Minnesota with more than 60 percent of the vote.