Joe Manchin Leaving The Democratic Party Is The Best Thing That Could Happen To Them

It's possible that this story from David Corn is just Sen. Manchin trying to scare Sen. Chuck Schumer and President Joe Biden into capitulating on the infrastructure bill, but there are more good reasons to call his bluff and let him leave than back down like a scared little bunny:

1. The Democrats will no longer have to listen to Manchin. Is there a chance that Manchin caucuses with the Republicans, giving them power over the Senate? Yep. But the Democrats still have the House of Representatives and the White House, so the GOP aren't going to be able to pass anything either. As powerful as Manchin will seem in the Senate, he will no longer be a factor in the overall process of lawmaking.
2. The Democrats can now run someone against Manchin in West Virginia. It's doubtful that they'll run someone like Paula Jean Swearegin, but any candidate who is to the left of Manchin economically would be an improvement. And let's not forget that Manchin pushed a gubernatorial candidate on West VA, who quickly changed from "D" to "R" after he won. Manchin leaving would give the party a rare opportunity to put someone more "party loyal" in the state. 
3. The end of "One Party Rule" may help Democrats in the mid-terms. Right now, the Democrats chances of surviving the 2022 midterms with any majority don't look good. It's easy to know why: they control the White House and Congress yet haven't lived up to their 2020 campaign promises. Losing the Senate will all but guarantee (more) gridlock, and if the Democrats are smart, they can parlay that into blaming Manchin and the Republicans. It might not save them from losing control of the House, but at worst it could mitigate the losses to the point where the GOP would be in the same boat as the Democrats are in now: arguing with themselves more than with the other party. 
4. It would save the "credibility" of the "progressive" Democrats. Sen. Bernie Sanders and his (somewhat) ideological counterparts in the House have been in freefall since Biden won. They could make all the big speeches and policy proposals under a Trump/GOP-dominated government, but when one of their own is in charge (and governs as conservatively as any regular Republican), it takes the wind out of their sails. Basically, Sanders, AOC, Omar and the rest are only allowed to criticize Biden, Schumer, Manchin, Sen. Sinema and Speaker Nancy Pelosi but so much (and in many cases, not at all). Manchin leaving allows them to be more vocal and adversarial, and (slightly) raises their "cred" by attacking someone who isn't technically a Democrat or a Republican (for once). 

Again, the likelihood of Manchin going through with this or the Democrats calling his bluff seems slim. In truth, having him play the Token Villain Teammate allows the party to collectively shrug their shoulders and tell their constituents that they wanted to do more, but just couldn't.