For the third time in the past year, the United℠ Explorer Card is dangling a bigger, two-part sign-up bonus in front of potential applicants. Depending on how much you spend, and how quickly, you can earn up to 65,000 bonus MileagePlus miles: Learn More You’ll earn a 40,000-mile bonus if you spend $2,000 in the... Paul Soucy is a writer at NerdWallet.