The American Dream’s promise of a better life if you work hard enough is fracturing.The big picture: Socioeconomic mobility in the U.S. is at its most sluggish in history. Not only are fewer Americans living better than their parents, but there’s also a growing number of people doing worse than their parents.By the numbers:The World Economic Forum released a report this week in Davos that ranked the United States 27th in the world for social mobility. The top five nations were Denmark, Norway, Finland. Sweden and Iceland.In a recent study, researchers from UPenn, Northwestern, the University of Nebraska and the Census Bureau looked back as far as 1850 and concluded that socioeconomic mobility in America is at its worst ever.Per the study, around 60% of people born in the 1940s did better than their parents, compared to 40% of those born in the 1980s.And just 15% of 1940s kids lived worse than their parents, compared to 30% of people born in the 1980s."Most parents expect that their kids will do better than them," says Xi Song, a professor at UPenn and one of the researchers. But now that happens for less than half of kids.There's a stark racial gap when it comes to mobility, Stanford law professor Ralph Richard Banks writes in a New York Times op-ed."Black boys who grow up rich are twice as likely as their white counterparts to end up poor.""And of those black boys who start life poor, nearly half will remain so in adulthood, while more than 2 in 3 of their white peers will escape the poverty of their youth."And mobility depends on where you grow up, too.As we reported earlier this week, kids' earning potential and life expectancy hinge on the neighborhoods where they were born."For moving from the bottom of the income ladder to the top, the South offers the worst odds in the United States," per NYT.On top of that, areas with low social mobility in the U.S. also have larger life expectancy gaps between the rich and the poor, per another UPenn study out this week.The bottom line: Worsening income inequality paired with stagnant socioeconomic mobility is defining today's America. And these trends will impact everything from public health to how people vote in 2020.Go deeper:Unemployment fell to 50-year low in 2019 but wages stagnatedAffordability is driving Americans' decisions on where to live