The British singer's "25" may be the second-biggest album of the millennium, but historic precedent and voter sentiment suggest that Beyoncé is the clear frontrunner for Grammy's top award.

The words "Adele" and "underdog" might not seem to go together in any known ­universe.

Her album 25 has earned 10.4 ­million equivalent album units in the United States, according to Nielsen Music, of which 9.2 million were in traditional album sales. The set finished both 2016 and 2015 as the year's best-selling album -- the first time one album has topped two years since Adele's previous album, 21, did it in 2012 and 2011. When it comes to 21st-century sales ­benchmarks, she is her own only serious competitor. Add to that 21 garnered six Grammys, including album, song and record of the year.

And yet 25 is considered ­something of a long shot for album of the year at the 2017 Grammys, taking place Feb. 12 in Los Angeles. How is that possible?

Partially, it comes down to competition, with Beyoncé's ­ultra-personal Lemonade far ahead in the critical cred derby (92 to 75, according to the Metacritic site). But another key factor is historical ­precedent. Once Grammy voters have bestowed album of the year on an artist, they tend to move on; only U2 and Taylor Swift have ­captured the prize twice since Stevie Wonder won three out of four years in the mid-1970s.

The historical record makes it easier to predict what won't ­happen than what will. And in the Grammys' 58-year history, no artist who has swept the album, record and song of the year categories has ever pulled off the triple crown again. If anything, fortunes have gone the opposite way: Of the three most recent acts to sweep, two -- Norah Jones and Santana -- weren't even nominated in any of those categories with their follow-up projects; the third, the Dixie Chicks, haven't released an album since their sweep a decade ago.

History aside, a more practical disadvantage for 25 in the album race may be that it came out on Nov. 20, 2015, 15 months before the 2017 Grammy telecast.

"An album that came out in 2015 might feel like a very long time ago," says one longtime member of The Recording Academy. "Plus, if you look at what's going on in the world [politically] and what Beyoncé is saying about it, Lemonade feels more fitting on several different levels," particularly for the left-leaning voter base.

As a consolation prize of sorts, Adele's "Hello" is favored for both record and song of the year. "Record seems like a more conservative category anyway," continues the Recording Academy ­member, "and everybody liked 'Hello,' whether or not they loved 25."

But the song, too, faces the Grammys' ­historical reluctance to indulge in reruns. Uniquely, U2 won the record category in 2001 and 2002 for songs from the same album -- "Beautiful Day" and "Walk On," both from 2000's All That You Can't Leave Behind -- but Roberta Flack (in 1973 and 1974 for "The First Time Ever I Saw Your Face" and "Killing Me Softly With His Song" ) and Simon & Garfunkel (in 1969 and 1971 for "Mrs. Robinson" and "Bridge Over Troubled Water") were the only artists ever to pull off wins for singles from consecutive projects. In the song category, only Flack, U2 and Bette Midler have had songs from successive albums take the prize.

Of course, Adele has many factors working in her favor to break Grammy precedent. For one, she had such a long gap between album projects -- nearly five years -- that voters may not see any fatigue factor. There's also the possibility of vote ­splitting among the other contenders for album of the year. Factoring out the likely long shots (Sturgill Simpson, Justin Bieber), that leaves Beyoncé and Drake as Adele's toughest competitors. Both are formidable in terms of commercial impact: Drake's Views was 2016's No. 1 album with 4.1 million equivalent album units, compared with 2.4 million for 25 and 2.2 million for Lemonade. Factor in the critical and cultural adoration factor for Beyoncé to give her a Grammy boost over Drake. But those two albums have significant overlap in their appeal to an R&B/hip-hop demographic and could conceivably split the vote.

For the most traditionally minded voters -- the type who coalesced to give Steely Dan a win over Eminem in 2001 and Herbie Hancock over Kanye West and Amy Winehouse in 2008 -- Adele may seem like the only choice. But Beyoncé's wide appeal suggests that even if those members favor Adele, it won't be a unilateral vote.

"I tend to look at it on a chapter-by-chapter basis, looking at what's going on in those cities," says one Recording Academy insider. "Of the 12 chapters, the three largest are Los Angeles, New York and Nashville, and they'll split between Adele and Beyoncé. So will Seattle and San Francisco, probably. But then you've got Chicago: Look at what's going on there and tell me they won't vote for Beyoncé," as will, the member believes, Louisiana-Memphis [a combined chapter], Philadelphia, Atlanta and Miami. And as a Houston native, "she'll probably split some of the Texas vote with [country-leaning] Simpson."

The Grammys may be the real winner if a split places photos of Beyoncé and Adele on the nation's front pages the next day. "Adele will more than get her due," says one voter, "and the Grammys like to give album of the year to the person who really opened up a personal journal. Last time, that was Adele, but this time it was Beyoncé." Another adds: "I think a lot of people feel we're overdue to really reward Beyoncé for her Beyoncé-ness."

This article originally appeared in the Jan. 28 issue of Billboard.