Six months into a long-awaited Republican administration with no major legislative accomplishments to show for it, GOP leaders in Congress are anxious to get a move on—so much so that senators are preparing to vote next week on a motion to proceed on a health care measure without knowing, exactly, what it will entail. Waiting for all the details ahead of time, Majority Whip John Cornyn told reporters, is a "luxury we don't have."

Republicans have spent the past seven years and multiple election cycles pledging to repeal and replace Obamacare. The election of a GOP president, they argued time and again, would be the final puzzle piece. Now, with Donald Trump behind the Resolute Desk, the health care debate has become a proxy for credibility and governance.

In other words, if Republicans can't make good on a signature promise—one that has been akin to an organizing principle for the base—how can they sell the party to voters?

As lawmakers consider voting for legislation that is unpopular and is projected to leave roughly 22 million uninsured, according to analysis by the Congressional Budget Office, they are also weighing the political fallout for the party if they don't proceed with it.

"Failure is not an option," Texas Sen. Ted Cruz, who is up for re-election next year, said after a meeting at the White House with his colleagues.

Florida Sen. Marco Rubio, who like Cruz also ran for president, insisted that Republicans would eventually replace Obamacare. "It may not happen this week or next week, but it’s going to happen," he said. "We have at least 51 people here who promised to do it, and we intend to keep that promise."

The health care measure is key to the GOP agenda, as it was designed to pave the way for tax reform. And while congressional committees are already at work on tax policy, a failure to resolve health care bleeds into the remainder of the party's agenda.

"There's no question this is a long held promise that virtually every Republican has made to voters, so it does have significant consequences if given the opportunity and they and can't get it done," said GOP strategist Josh Holmes, a former aide to Sen. Mitch McConnell, majority leader. "The biggest problem Republicans could face in 2018 is an ongoing narrative that they are unable to govern."

Conservative outside groups have banded together to pressure Republicans into fulfilling their campaign pledges, arguing that a failure to do so would depress the party base in the midterms. "They are going to need to call hospice because their control [of Congress] is not long for this world," Club For Growth President David McIntosh said.

Brent Bozell, president resident of the conservative Media Research Center, said conservative voters are going to blame Republicans—not the opposing party—for failure. "If they feel betrayed and have no reason to vote, they won’t vote," he said.

That prospect is also starting to weigh on House lawmakers, some of whom have expressed concern that Senate inaction might take a toll on members beyond the upper chamber.

“Senators have now wasted seven months doing nothing," said Florida Rep. Dennis Ross. "The American people are sick of the excuses from senators. I’m sick of the excuses."

Ross and other critics have argued that Republicans risk being inconsistent and dishonest after having voted multiple times to repeal the law while Barack Obama was president.

"I’m frustrated in general that my party wasn’t more consistent," Sen. Rand Paul, whose opposition to proceeding on the original Senate bill helped derail it, told Bloomberg News. "We ran and won in four elections—voters rewarded us saying you’re for repeal. Now we have a Republican president, they seem to have gotten a bit weak in the knees. "

Jenny Beth Martin of Tea Party Patriots said the reluctance on the part of a large handful of senators represents the politics Trump ran against. Supporters "voted for Trump because they wanted a wrecking ball in D.C.—for this reason," Martin said.

The president, meanwhile, is eager for a win and has said he would sign any health care-related bill Congress sends to his desk. But he has also been of little utility during the process and hasn't seized the bully pulpit to sell the bill.

At times he has complicated the conversation by adjusting his own opinions on the legislation, varying from complete repeal without a replacement to completing both simultaneously, to letting the current law fail. During a luncheon with Republican senators at the White House on Wednesday, Trump chided Dean Heller, one of the most vulnerable party lawmakers up for re-election next year. "He wants to remain a senator, doesn't he?" Trump said, urging the Nevada senator to support the legislation.

During a later interview with the New York Times, Trump returned to a previous line. "If we don’t get it done, we are going to watch Obamacare go down the tubes, and we’ll blame the Democrats," he said.

But Republicans on Capitol Hill don't think that option will work. "I don’t want to see that," said Wisconsin Sen. Ron Johnson, arguing for immediate steps to stabilize the insurance markets. Asked whether Republicans would suffer politically if they failed to keep their pledge to repeal the law, Johnson said the environment and challenges have evolved.

"We’re dealing with a really big mess, and it’s very complex, and we’ve got a big spectrum of people in our party," Johnson said. "The condition today is different than it was seven years ago, or four years ago. It does complicate things that these markets are collapsing, they’re in a further state of decay, so you are confronted with the reality of today and it’s just complex."

For his part, Trump has dismissed criticism of a stalled agenda, even though he pledged during the campaign to replace Obamacare quickly. "I am not in here six months, and they’ll say, ‘Trump hasn’t fulfilled his agenda.’ I say to myself, wait a minute, I’m only here a very short period of time compared to Obama," he told the New York Times, referring to the 14-month timeline to pass the Affordable Care Act.

The president has also argued that Democrats had a larger majority in the Senate during the passage of Obamacare and suggested voters would need to elect more Republicans in the midterms. The suggestion ignored the fact that Republicans only need a simple majority for passage of health care reform, given certain parliamentary procedure on the measure.

"We need to have some accomplishments and some wins, and if we aren’t able to do that it will be a drag in 2018," said a Republican operative familiar with congressional campaigns.

While Republicans are only defending two competitive Senate seats this cycle, they hope to expand their majority by defeating Democratic incumbents in states Trump won. That task becomes harder if Republicans have little to sell by way of governing. Vulnerable Democrats in the Senate, meanwhile, have stood opposed to the Republicans' health care reform efforts, signaling how potent they figure the issue will be in the midterms.

A Kaiser Health tracking poll this month found 71 percent of Americans would rather see Republicans work with Democrats to fix Obamacare without repealing it. While a majority of Republicans want the GOP to continue with its repeal plans, Trump supporters are split on the issue.

Elsewhere, there are mixed signs for Democrats. A Washington Post poll released this week found that registered voters would rather see the next Congress controlled by Democrats than Republicans by a 52-percent-to-38-percent margin. But by a 65-percent-to-57-percent margin, Republicans said they were more likely to vote in the midterm elections than Democrats. Additionally, 51 percent of voters said Trump would not factor into their midterm election vote.

These numbers, in addition to the high support Trump has among GOP voters, help explain why Republicans are pointing fingers at each other and not at the president—yet.

If congressional Republicans are unable to notch major accomplishments, including health care, GOP candidates running to challenge Democrats might start using the language of the president. "If Trump is still seen as a guy trying to make change,” the Republican operative said, "You’re going to run against Washington and run as closely to Trump as possible."