Frontrunner Joe Biden faced repeated criticism on multiple fronts Thursday from his Democratic rivals for the 2020 presidential nomination, including calls to leave the battle to oust Donald Trump to a younger generation.

In a sometimes scrappy showdown of the Democratic heavyweights, Senator Kamala Harris landed several blows on Biden in the second of two nationally televised debates, putting the former vice president on the defensive as he argued that he is best-positioned to take on the Republican president.

Biden blasted Trump for his "horrible" policies that have exacerbated income inequality, while his chief rival for the nomination, Senator Bernie Sanders, took it directly to the "phony" president, calling him "a pathological liar and a racist." 

But 76-year-old Biden also found himself on the receiving end of a pointed attack from a lower-tier candidate half his age.

Congressman Eric Swalwell, 38, on Thursday called on him to "pass the torch" to a new generation better equipped to tackle climate change, expand health care coverage and reduce gun violence.