Republicans will be tested today on the strength of party unity in the Trump era and their party's ability to deliver on the promises they've made to the voters that sent them here.

"This is our chance and this is our moment. It's a big moment," House Speaker Paul Ryan told reporters earlier this week. "And I think our members are beginning to appreciate just what kind of a 'rendezvous with destiny' we have right here."

The moment is particularly defining for Ryan, the reluctant speaker who is facing the toughest legislative battle of his nearly 20-year congressional career. "One of the reasons I don't want this bill to fail is I don't want Paul to fail," said Rep. Mike Simpson, R-Idaho, an ally of the speaker who supports the bill.

The speaker has put the full weight of his office behind passing legislation that goes much further to repeal and replace key pillars of Obamacare, to remake Medicaid into a block grant program that caps federal spending. The entitlement program predominantly helps the poor and currently has an open-ended funding stream.

It's the kind of conservative reform that Ryan has jokingly said he's dreamed about since his keg party days, but it might not be enough — even with Republicans in control of both chambers of Congress and the White House.

The House Freedom Caucus, a bloc of about 30 hard-line conservatives, maintain going in to today's scheduled vote that they have enough members on their side to defeat the bill. Their opposition has not softened, despite continued efforts by President Trump, Vice President Pence and their senior White House aides to grant concessions and cajole lawmakers from districts Trump won by big margins last November.

"We're being asked to sign a blank check and hope it works out," said Rep. Scott Perry, R-Pa., a member of the Freedom Caucus, "And in the past that hasn't worked out real well for this process, so I think we're right to be skeptical."

Perry was one of about 25 Freedom Caucus members who huddled with Vice President Mike Pence and White House adviser Kellyanne Conway on Wednesday. It didn't change his vote. Conservatives like Perry want the bill to go even further to repeal President Obama's health care law. Specifically, these conservatives want assurances the final bill would ultimately repeal the essential health benefits included in the Affordable Care Act, which cover 10 categories of health services insurance plans must cover, including prescription drugs and prenatal care.

"We want free market competition and how can you have free market competition when the government is mandating what's going to be included?" Perry said. Conservatives argue that eliminating the essential health benefits will allow insurance companies to offer cheaper insurance plans with more tailored coverage. Opponents say it will only increase out-of-pocket costs for consumers.

Conservatives also received some political cover from outside conservative activist groups like Heritage Action and FreedomWorks, which came out in opposition to the bill.

The network of political action groups funded by Charles and David Koch, wealthy libertarian-minded donors who have not supported Trump, are putting money behind their opposition to the bill. Two Koch-funded groups, Americans For Prosperity and Freedom Partners, announced last night they would establish a seven-figure fund "to stand by principled lawmakers who keep their promise of fully repealing Obamacare by opposing the American Health Care Act (AHCA) unless there are significant changes." It amounts to a promise of protection for members who might fear a primary challenge for breaking with Trump.

As the day unfolded yesterday, it became clear that conservatives were not the only weak link in the vote count. With every new "yes" vote announced, a "no" vote would appear. Reps. Lou Barletta of Pennsylvania and Steve King of Iowa announced they would support the bill on Wednesday, but their support was offset by fresh opposition from lawmakers including Don Young of Alaska, David Young of Iowa, and Frank LoBiondo of New Jersey.

The trio of opponents are mainstream Republicans, the kind of rank-and-file members party leaders can usually rely on to pass their agenda. But the policy in the GOP bill, the American Health Care Act, would disproportionately affect older, poorer Americans — the very constituents who make up many GOP lawmakers base of support back home.

For instance, LoBiondo said in a statement that his South Jersey district and its retirees would suffer under AHCA. "Three South Jersey counties have more than 30% of their residents receiving Medicaid assistance. Medical professionals--our hospitals, doctors, nurses — are opposed," he said.

The speaker focused on more moderate members of the GOP, working members during House votes on Wednesday and holding one-on-one meetings in his office throughout the day.

"If you don't recognize how much is on the line, you haven't been paying attention," said Rep. Tom Cole, R-Okla. He supports the bill and, like many lawmakers, remained optimistic that the votes would come together to pass it. Cole even suggested they might have to win the vote on the floor. "You never know about these things until you actually get to the vote," he said.

With five vacancies in the 435-member House, Republicans can lose 21 votes and still pass the bill. Every Democrat is expected to vote against it. House Republicans enjoy one of their largest majorities in decades, so the 21-vote cushion is much larger than past GOP-controlled congresses have enjoyed.

Cole said most Republicans were aware of the importance of this vote: "It's a very consequential vote. It really is: 'Can you govern or can't you?' "

For their part, Democrats are unified against the bill, which undoes President Obama's signature domestic achievement. Former Vice President Biden returned to Washington to voice his opposition to the bill at a rally outside the U.S. Capitol.

"Look, folks, here's the deal: When you cut to the chase, we're talking about eliminating close to a $1 trillion in benefits that go to people to be able to meet the commitment we made that health care is a right, and we're transferring all of that to the wealthy," Biden said. "That's what this is all about, it's about a transfer tax, basically. Eliminating the Affordable Care Act means eliminating an awful lot of things that people need."

If the House approves the bill on Thursday, the thrill of victory will be short-lived. The bill still needs to pass the Senate, and it faces a new round of opposition and legislative hurdles in that chamber. The bill then would need to back to the House again to approve any Senate-passed changes before it could go to Trump's desk.

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