(CNN) The latest late push by Republicans to kneecap Obamacare is teetering after Sen. John McCain's decision to oppose it . But the past week's outbreak of internecine brawling underlines a raft of unresolved tensions. Among Democrats.

As recently as 10 days ago, it appeared the party was angling further down the long road to post-2016 reconciliation. When Sen. Bernie Sanders introduced his new "Medicare for all" bill on Capitol Hill on September 13 , he was flanked by a collection of the party's most promising 2020 prospects. A third of the Senate Democratic caucus had signed on, and the detente forged by the battle to protect Obamacare was looking increasingly durable.

But that brief era of good feelings quickly cracked up under pressure from Republicans. When the majority began plowing ahead with the Graham-Cassidy bill, another controversial plan to radically overhaul the American health care system, Democrats began to lash out -- first and primarily at the GOP, but then, as its momentum grew, one another.

Most of the venom was directed at Sanders. First, for choosing to unveil his bill before a September 30 Senate deadline, when the window closes on the GOP's ability to pass a measure with a simple majority. Then, when it was announced on Thursday afternoon that Sanders, along with Minnesota Sen. Amy Klobuchar (a Democrat who did not back the "Medicare for all" bill), would square off with Republican Sens. Bill Cassidy and Lindsey Graham, in a CNN health care town hall next Monday night.

"Bernie likes to paint himself as the warrior of the many, but in truth, I think he's fighting for a constituency of one," a Democratic operative said in an email. "With McCain's vote still up in the air, and Sanders eagerly volunteering himself as precisely the foil Republicans need, I'm a bit worried Lindsey Graham might have a new (best friend for life) in the Senate."

Sanders' critics mostly refused to go on the record with their gripes. Obama alum turned podcast host Tommy Vietor was a rare high-profile exception, tweeting, "I'm not sure single payer vs Graham-Cassidy is the debate we want right now." Both on the merits of the criticism -- and its framing -- Sanders allies were infuriated.

"This orchestrated campaign, which is coming from some people who are hostile to the very idea of guaranteeing health care for all is disgraceful," National Nurses Union communications director Chuck Idelson said when party people began to question the timing of his single-payer rollout. "It clearly reminds people of the type of attacks that occurred against Bernie Sanders during the (2016 Democratic) primary and a lot of us are pretty disgusted with it."

There is no evidence of coordination, but Idelson said "the pattern (of attacks) is a reminder of what a lot of us witnessed last year."

Sanders spokesman Josh Miller-Lewis pushed back testily on Twitter. "This (CNN) debate," he wrote, "is about exposing Graham-Cassidy as the most destructive piece of legislation in the modern history of our country." (He also retweeted a pair of graphs comparing Sanders' favorability, favorably, to Graham's.)

On Friday morning, just before McCain's announcement, Miller-Lewis said Democrats were off-base in questioning Sanders' dedication to protecting Obamacare.

"Sen. Sanders does not need to be lectured about the importance of defeating the Republicans' latest attempt to take health care away from 30 million Americans," he said in an email. "Since January, he has organized more than 170 rallies, spoken to tens of thousands of people and gone to 12 states to defend the Affordable Care Act."

The Monday night event, Miller-Lewis argued, presented a unique opportunity for Sanders and Klobuchar to highlight troubles with the Republican bill.

"At a time when few people understand how destructive and immoral Senators Graham and Cassidy's legislation is," he said, "Sanders and Klobuchar intend to educate the American people about the devastating impact it will have on our health care system and our people."

Whether or not they get the chance -- or what the debate on Monday night ends up looking like -- the stains of the past few days are bound to linger.

In fact, it's quite clear they've never gone away.