While gun sales have been climbing for decades — they often spike in election years and after high-profile crimes — Americans have been on an unusual, prolonged buying spree fueled by the coronavirus pandemic, the protests last summer and the fears they both stoked.In March last year, federal background checks, a rough proxy for purchases, topped one million in a week for the first time since the government began tracking them in 1998. And the buying continued, through the protests in the summer and the election in the fall, until a week this spring broke the record with 1.2 million background checks.