Sen. Joe Manchin on Sunday called on Joe Biden to end his reelection campaign, the latest domino to fall in a broader Democratic upheaval over the president's ability to win this November.

Manchin, I-W.Va., who caucuses with Democrats but left the party earlier this year, told "This Week" co-anchor Martha Raddatz that he came to the decision "with a heavy heart," but that the swell of Democrats issuing similar calls after last month's debate made the current situation untenable for Biden.

"The first week after the debate, I thought the president needed time to evaluate and make a decision if he was going to at that time, and then I thought, well, we'd hear from my colleagues who are in very difficult, challenging areas of the country, whether it be in Congress, as far as their districts, or in the states, as far as my senators, and they're speaking out now. And then when you see the donor class, basically, speaking up and saying that they went a different direction, if you will," he said.

Manchin argued that dropping out now would allow Biden to tackle a litany of issues he's prioritized, including uniting the country, ending fighting in Gaza and helping Ukraine fend off Russia's invasion, on top of being "able to show the rest of the world the orderly transfer of power from the superpower of the world."

"He will go down with a legacy unlike many people, as one of the finest and truly a [patriotic] American," Manchin said. "So, with that, I come with a heavy heart to think the time has come for him to pass the torch to a new generation."

This is a developing story. Please check back for updates.