Even the face of GOP moderation, Maine Sen. Susan Collins, initially expressed more openness to the so-called Graham-Cassidy bill than Paul had. Paul has written op-eds trashing the plan, launched tweetstorms dismissing it as “Obamacare lite,” and in case he wasn’t clear, gone on TV to reiterate his Lone Ranger stance.

That’s made Paul persona non grata in the Senate Republican Conference these days.

“If you vote against us, you’re voting to keep Obamacare,” said Sen. Bill Cassidy of Louisiana, one of the bill’s namesakes, when asked about Paul’s intractable stance. “Period. End of story.”

“It just makes no sense,” griped another GOP senator. “It just makes me want to pull my hair out that Rand Paul would team up with Susan Collins to defeat this bill.”

Even President Donald Trump piled on Paul, tweeting Wednesday: “Rand Paul is a friend of mine but he is such a negative force when it comes to fixing healthcare. Graham-Cassidy Bill is GREAT! Ends Ocare!”

Interviews with more than a dozen Senate Republicans showed varying degrees of frustration with Paul’s latest crusade. Since the Obamacare repeal effort began this year, he has remained one of the most consistent headaches for GOP leadership in its quest for the elusive 50 votes to dismantle Obamacare.

Paul is also drawing opposition from the anti-abortion lobby, a reliable ally. Susan B. Anthony List President Marjorie Dannenfelser said Paul’s “outright opposition to the bill and his dismissiveness of the pro-life priorities within it is alarming and damaging” and called his stance an “unacceptable position for a pro-life Senator to have.”

Sergio Gor, a spokesman for Paul, replied: “There is no one more pro life then Senator Rand Paul.”

Paul has repeatedly pressured the conference to go in a more conservative direction when it comes to ending Obamacare. He proposed a straight repeal of the 2010 law without a replacement, but that effort failed on a 45-55 vote in July, with seven Republicans voting against Paul’s amendment.

He also started the effort to replace the law at the same time it was repealed, though over the past few weeks he has wavered on that stance. He ended up voting in favor of the so-called skinny repeal effort that collapsed in July.

Trump has spoken to the Kentucky senator privately about the latest repeal effort, but to no avail. Republican leadership doesn’t even appear to be trying to convince him. Cassidy has tried nudging Paul, but it hasn’t worked.

“He takes himself out of the discussion very early on and it’d be nice to have him,” said South Dakota Sen. John Thune, the third-ranking Senate Republican. “When you only have 52 to start with, every one of them matters. And it obviously makes it more challenging and more difficult, because we gotta figure out a way and we got other members, who, as you know, have issues.”

Not all Republicans are irritated with Paul’s opposition. Senate Finance Committee Chairman Orrin Hatch of Utah said Paul “has the right to vote the way he wants to,” calling Paul a “hard worker and a good guy.”

But Paul is alone even among his usual conservative cohorts in the Senate. Sens. Mike Lee of Utah and Ted Cruz of Texas, who also have prodded GOP senators to go further to the right in their Obamacare repeal efforts, are warming to the legislation from Cassidy and Sen. Lindsey Graham of South Carolina.

But to Paul, his opposition to the Graham-Cassidy measure is a perfectly principled stand. The Graham-Cassidy plan would leave the crux of Obamacare intact, he argues, and that’s simply not good enough for a party that has promised to nix the Democratic health care law.

The Kentucky senator has rattled off a litany of complaints about Graham-Cassidy, saying it would just redistribute a mountain of federal cash from states that expanded Medicaid under Obamacare to states that chose not to. Because Republican states would largely benefit at the expense of Democratic ones, Paul said Tuesday, it essentially amounted to “petty partisanship.”

When pressed on the criticism from fellow Republicans that he was merely helping Democrats to keep Obamacare the law of the land, Paul responded: “Yeah, well, these people would be confused.”

“There’s probably been no louder voice of repeal of Obamacare than myself,” Paul said. “I’ve not only advocated for it, I’ve introduced bills to replace it with market reforms. So I think I’ve done yeoman’s work in trying to repeal it.”

GOP leaders have not yet tried to flip Paul. Senate Majority Leader Mitch McConnell is instead focused on working over Collins, as well as Sens. John McCain of Arizona and Lisa Murkowski of Alaska, other key holdouts.

“It’s his decision to make,” said Graham, who noted that Cassidy has spent time trying to convince Paul. “I think we get 50 votes without him.”

The bill would transform Obamacare spending into block grants for the states and impose deep cuts to Medicaid in the coming years, while dismantling the health care law’s coverage mandates. Democrats are uniformly opposed to the Graham-Cassidy measure, despite Graham’s insistence that some conservative states represented by moderate Democrats stand to benefit from his bill.

The bill is the Senate GOP’s best opportunity to repeal Obamacare before a key procedural tool that allows Republicans to avoid a Democratic filibuster that expires at the end of the month.

Paul, of course, has a long history of being a thorn in the GOP leadership’s side to take a stand, even when he’s destined to lose. Earlier this month, Paul demanded — and received — a vote on an amendment that would offset the $15 billion set aside for hurricane aid. That failed on a lopsided 10-87 vote.

A week later, Paul threatened to hold up a sweeping defense policy measure until he got a vote on his proposal to repeal the 2001 and 2002 authorization of the use of military force that have been the basis for the ongoing war on terror. That too was set aside, on a 36-61 vote.

“I think most of us are trying to figure out what the logic is,” Sen. Mike Rounds (R-S.D.) said of Paul’s opposition to the latest Obamacare repeal push. “We all know that some folks would rather have a bill that’s perfect. But I guess if we can’t have a bill that’s perfect, I’d rather have a bill that’s much better than what [the law] is today.”

Sen. Thom Tillis (R-N.C.) pointed out that Paul has said this measure is only 10 percent repeal, but added: “So, a ‘yes’ vote for this bill 10 percent repeal. A ‘no’ vote is 100 percent support” for Obamacare.

Asked whether he feels pressure from fellow Republicans amid all their criticism, Paul shrugged and answered: “Uh, no.”

“I feel very comfortable and this is what I promised people,” he said. “When I go home, I feel reinforced by the voters.”