(CNN) Donald Trump's top campaign promise of repealing Obamacare remains unfinished as the President heads into Washington's sweltering summer months.
With the Republican Party's most pressing undertaking stuck in limbo, GOP senators and aides are beginning to wonder about one undesirable outcome: that the Senate takes a vote on a health care bill in the coming weeks knowing full well it could fail.
RELATED: Conservatives say they're losing health care bill fight
Republicans are attempting to use the so-called budget reconciliation process, which would allow them to avoid a Democratic filibuster. With only 52 Republicans in the Senate, however, there is no room for error as leaders struggle with the daunting task of finding consensus between their caucus' moderate and conservative flanks on such a deeply divisive issue.
Last week, it became clear that GOP leaders were seriously considering several moderate concessions on their health care bill, including keeping some of the Obamacare taxes and not allowing states to repeal what is known as community rating -- a key protection for people with pre-existing conditions.
The negotiations are hardly over, but the information that has trickled out from lawmakers have conservatives on and off Capitol Hill on edge and watching Majority Leader Mitch McConnell for clues.
Bill text could go to the Congressional Budget Office early this week as well for its analysis.
"It might be that McConnell knows he can't get to 50 so he's going as far left as possible to give moderates cover when they do vote for this bill," one conservative Senate aide said.
So why vote on a bill that may not pass?
The issue could jeopardize other top-ticket items on the GOP's agenda, Utah's former Republican Gov. Mike Leavitt told CNN.
Trump has pressed Republicans in Congress to move ahead with other priorities, including tax reform and infrastructure.
"There's some skepticism as to whether they can get (health care) done. And they don't want to waste the rest of the legislative year," said Leavitt, who served as Health and Human Services secretary under President George W. Bush.
"There has to be a moment when you say, 'We've got to do something and this is the moment.' ... Either put up or stop," he added.
If Senate Republicans bring up a bill designed to appease the more moderate members in its ranks, that strategy would mark a sharp departure from the path that House Republicans chose to take last month.
As it struggled to get the votes needed for passage, House leaders made significant concessions to win over some of the conference's most conservative lawmakers.
One provision gave states the choice of opting out of the requirement that insurance companies cover so-called 10 "essential health benefits," as is currently mandated under Obamacare. Another last-minute add allowed insurers to charge people with pre-existing conditions more if they let their coverage lapse.
But in the Senate, GOP leaders appear more willing to craft a bill that soothes their more moderate colleagues -- at least for now.
One of the key departures Senate leaders are eying is giving federal money to Medicaid expansion states for longer. Sen. Rob Portman, a Republican from Ohio, has proposed a seven-year "glide path" that would more gradually phase out the federal match funds.
Another option on the table would make the tax credits offered to help people buy insurance more generous for lower-income Americans. Those tax credits already attracted the ire of some Senate Republicans, who dismissed them as little more than "Obamacare lite."
There has been some concern, however, that conservatives could also face another loss when it comes to those tax credits. In the House bill, Republicans were able to include language that barred the federal tax credits from being used to purchase insurance that included abortion coverage in most cases. However, under Senate rules -- which only allow budgetary changes to be accepted under the reconciliation process -- it's not clear that Republicans could pass that same language.
While conservatives may not be pleased with the changes on the table, moving the bill to the left could help McConnell protect his most vulnerable members. There aren't many endangered Republican members up in 2018, but those who are hail from more purple states, like Dean Heller in Nevada and Jeff Flake in Arizona.
Republican Sen. John Thune of South Dakota said last week that it is important for the Senate to try to pass a bill in the next few weeks, even if the vote fails.
"I still think in the end there is a huge reason why we have to get to 50 on this," said Thune, the third-ranking GOP leader in the Senate. "Obviously, we're going to have a vote on this one way or the other. But if we don't pass something and we go into '18, you know, it's on us to try to get this fixed."