(CNN) As Republicans scramble to tamp down fears that their health care bill would gut protections for sick people, they're running into a chorus of opposition -- from fellow Republicans.

With direct orders from President Donald Trump to fulfill the GOP's years-long promise to repeal Obamacare, House Republican leaders are trying yet again to get the 216 votes they need to pass a bill this week. Thus far, they're failing.

The biggest problem: The legislation would let insurers charge people with pre-existing conditions more for their health care if those people let their insurance lapse at any point.

It's an ironic twist in the Republican Party's crusade to gut the Affordable Care Act, the landmark health care law enacted by former President Barack Obama in 2010. A major pillar of the law is the ban on insurance companies from discriminating against people based on their past medical conditions.

Now, even some of the very Republicans who have long vowed to dismantle Obamacare acknowledge that that protection is simply untouchable.

"From day one, I've supported the rights of those with pre-existing illnesses to be covered, and in my view this undermines that effort, and I can't be a part of it," GOP Rep. Fred Upton of Michigan told reporters Tuesday. "Yes, there are ways to fix it. But the proposal that's on the table now doesn't work."

Upton, the former chairman of the House's Energy and Commerce Committee, will oppose the bill, a significant blow to the GOP leadership.

He and Rep. Billy Long of Missouri plan to meet at the White House Wednesday morning in hopes that an amendment on pre-existing conditions could be negotiated.

Even Republicans who say they are inclined to support the latest House proposal are haunted by the concerns raised by constituents with medical histories.

In a strikingly candid and extended conversation with reporters in the ornate House Speaker's Lobby Tuesday afternoon, Rep. Tom Rooney of Florida said he has confronted "extremely angry" and "sincerely scared" constituents back home.

"You know, the most sincere anger I've noticed comes from people that are sincerely scared, people that may have a pre-existing condition that feel like they're about to lose it and they're going to die, and they're going to die because of a vote that we might be taking," Rooney said.

"And if we cannot explain to people that that is not going to happen, then it is going to be very difficult to ever bring a bill to the floor," added Rooney, who said he is leaning towards voting for the bill.

It's a sales pitch the GOP leaders aren't winning.

"Pre-existing conditions are in the bill. And I mandate it. I said, 'Has to be,'" Trump said on CBS's "Face the Nation" Sunday.

In another interview with Bloomberg News, Trump went as far as to claim that the GOP legislation "will be every bit as good on pre-existing conditions as Obamacare."

But the math is still not there.

The concern over pre-existing conditions has been so pervasive that CNN's whip count has 22 House Republicans who have publicly said they would vote against the health care bill. If 23 Republicans defect, the bill would likely fail a floor vote.

Democratic supporters of Obamacare say the GOP's struggle to repeal it validates the law's merits.

"The injustice of how people with pre-existing conditions had been treated before the Affordable Care Act was its biggest selling point. It's a concern that cuts across lines of race, class and geography," said David Axelrod, Obama's former senior adviser and a CNN contributor.

"By tampering with this fundamental element of the law, the Republican leadership and White House have touched the third rail of health care politics," he added.

The hard-to-swallow reality for Republicans, Axelrod said, is this: "It's very hard to dismantle the ACA and preserve its protections for people with pre-existing conditions."

GOP whip effort

Republican leadership is engaged in a frenzied whip effort, talking with members and educating them in hopes they can get rank-and-filers comfortable with the protections that do exist in the bill for people with pre-existing conditions.

Vice President Mike Pence was on Capitol Hill Monday and Tuesday talking with Republicans about their concerns, and lawmakers have also been speaking with Health and Human Services Secretary Tom Price.

For decades prior to the enactment of the Affordable Care Act, many Americans were unable to even afford or obtain insurance because of their past medical history. As Obamacare has shifted that norm, Republicans have grown increasingly careful in recent years to say they would not repeal protections for people with pre-existing conditions, wary of being branded the party that wants to take that protection away.

While Republicans have campaigned aggressively to dismantle Obamacare, there has been a quiet recognition that gutting protections for people with pre-existing conditions might be a political bridge too far. Even in the GOP's 2015 repeal bill that was ultimately vetoed by Obama, Republicans didn't try to repeal the protections.

That bill was mostly a message effort, however, as Obama's veto was guaranteed. This spring, Republicans have majorities in both the House and Senate, and a President excited to repeal Obamacare.

"Before 2014 it was all theoretical, but now it is actual people," said Rep. Larry Levitt, a health care policy expert at the Kaiser Family Foundation.

"As a kid, I was adamant that I didn't like broccoli no matter how good it was for me but, as an adult, I eat it all the time," said Jesse Ferguson, a former Hillary Clinton aide now working with Democrats to oppose Obamacare repeal. "After spending years adamant about repealing health care, part of the GOP seems to be growing up, ready to eat their broccoli and stop repealing the law because it's good for us."