Now should be their time in life to grab the reins, but when it comes to the 2020 presidential field, Generation X candidates are becoming an endangered species.The big picture: All the frontrunners in the still-crowded Democratic field are either Millennials (Pete Buttigieg, 37), Baby Boomers (Elizabeth Warren, 70), or products of the Silent Generation (Joe Biden, 77, and Bernie Sanders, 78). At 73, President Donald Trump is one of America's oldest boomers. Driving the news: The departures of Kamala Harris (55) and Steve Bullock (53) this week from the Democratic nominating contest are just the latest examples of the failures of Gen X to gain traction.Beto O'Rourke (47), Kirsten Gillibrand (52), Tim Ryan (46), and Seth Moulton (41) are earlier casualties.Hanging in the contest but at 3% or lower in national polls: Gen Xers Cory Booker (50), Julián Castro (45), Andrew Yang (44) and Michael Bennet (55). (Amy Klobuchar, 59, and John Delaney, 56, are boomers. Tulsi Gabbard, 38, is one of the oldest Millennials.)Harris was born in October 1964, and Bennet in November 1964, on the bubble between Gen X and boomer, but culturally they have more in common with the experiences of Gen X.What's next: Two late entrants, who jumped in last month after concluding the Democratic field just might not have what it takes, are either boomers (Deval Patrick, 63) or from the Silent Generation (Mike Bloomberg, 77).Bloomberg and another candidate, boomer Tom Steyer (62), are billionaires, so they can afford to stay in the race until the convention regardless of polling.By the numbers: Generation X generally describes people born 1965-80 — putting them between the ages of 39 and 54 — per the Pew Research Center. The Silent Generation covers birth years 1928-45.Baby Boomers were born 1946-64.Millennials were born 1981-96.Generation Z includes people born between 1997 and 2012. While some Zs can vote next November, none is yet old enough to run for president. Why it matters: Other generations might argue, it doesn't. (Ouch!) Gen X is a smaller pack population-wise than either boomers or Millennials.The New York Times summed it up as a "gloomy, goofy club of forgotten middle children," while a Washington Post columnist made the case that Gen Xers have been underrated "repairers," "fixers" and "uniters."Flashback: In cycles past, being in the age range that now covers Gen X was a sweet spot for presidential candidates.Bill Clinton was elected at 46. Barack Obama was 47. George W. Bush was 54. (You guessed it. They're all boomers.)Our thought bubble: As Lelaina Pierce said, "I was really going to be somebody by the time I was 23."