Washington DC - Another senator on Sunday joined calls for President Joe Biden to end his candidacy in favor of a younger Democrat, while a shock poll from the swing state of Michigan illustrated the growing sense that he will lose to Donald Trump if he stays in the race.

"I come [to this decision] with a heavy heart, but I think it’s time to pass the torch to a new generation," Senator Joe Manchin, a former conservative Democrat turned independent from West Virginia, said on ABC's This Week.

The call from a longtime friend of the president reinforced a swell of increasingly urgent pleas from top party officials for the 81-year-old Biden to step aside as signs mount of his eroding support.

Biden's ability to fight back has been limited; he has been isolating himself with Covid at his Delaware home since Wednesday, his health is said to be improving but his public face is limited to a series of attacks on Trump on social media.

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Meantime, a new poll from the battleground state of Michigan – where Trump, his right ear bandaged from the recent attempt on his life, held a raucous rally Saturday – carried grim news for the president.

The poll, which began the day Trump was wounded at a Pennsylvania rally and ended as he was accepting his party's nomination in Milwaukee, found Trump leading Biden 49% to 42% in a state the Democrat carried four years ago by three percentage points.

The Epic-MRA poll showed Trump doubling his lead since the last poll on June 27, just before the presidential debate that proved disastrous for the president. The survey even gave Trump a narrow lead in metropolitan Detroit, which is normally safe Democratic territory.

Yet another poll, by ABC News and Ipsos, showed Trump enjoying his highest national favorability ratings in years – at 40%, up from the mid-30s – propelled no doubt by the successful Republican convention and a surge of sympathy following the attempt on his life.