(CNN) -- Negotiations to repeal and replace Obamacare are fully underway now in the US Senate, where Republican lawmakers are grappling with how they can find consensus between their moderate and conservative factions while still managing to get the 50 Republicans they need to gut the Affordable Care Act.

It's tough math and although it is early in the process, so far the GOP's health care working group -- a collection of 13 GOP senators -- has already encountered some of the same hurdles that hindered the House's efforts, which struggled for weeks to collect enough votes to pass.

After last week's negotiations, which included two official GOP health care working group meetings -- one on the future of Medicaid and another on Obamacare regulations -- one Republican aide familiar with the talks said point blank they were "much less optimistic that something will get done" despite public statements about "productive meetings" coming from GOP senators.

Early predictions (and the hope of some House moderates) had been that the Senate's health care bill would quickly move to the left when it moved to the upper chamber, but behind the scenes, conservatives are acting as a powerful force.

In the middle of the action is Texas Republican Sen. Ted Cruz, a lawmaker who might once have been a thorn in the side of leadership, but now finds himself a key player at the negotiating table.

"That is not going to be easy," Cruz told reporters this week about the process, adding, "The conversations we are having are productive. We are seeing senators across the ideological spectrum, working to try to get to 'yes,' and that is exactly the inclusive process that we have to employ if we are going to get to a bill that commands the support of 50 senators."

Conservatives are making their case to leadership that to lower premiums, Republicans have to gut as many Obamacare regulations as the House bill did. On the chopping block are regulations that include things like the "essential health benefits," a regulation under Obamacare that requires insurers cover key medical costs like maternity care and prescription drugs. Some conservatives have suggested going even further than the House bill did, proposing that instead of allowing states to opt out of the regulations, the Senate would move to remove them altogether and then allow states to opt back in if they choose.

"I think we're going to leave it up to consumer to decide what they want to buy and what they need, so we're going to eliminate mandates, not add them," Texas Republican Sen. John Cornyn, the majority whip, told reporters when asked about the "opt in" option.

He added, "We haven't made any decisions. We're just batting around ideas."

Sen. Lamar Alexander, the chairman of the Senate's committee that oversees health care, floated another potential premium lowering idea in a closed-door meeting Thursday that would allow states to repeal Obamacare regulations if they automatically enrolled consumers in what is known as catastrophic coverage, a basic insurance package that would cover individuals in case of a serious health emergency.

But that spooked conservatives. A GOP aide familiar with the negotiations called the idea "corporatist single payer."

Republican senators involved in the effort emphasize that they are just getting started in the process and no decisions have been made yet.

"I'm still on the kind of 30,000 foot-level in terms of what are the primary goals of our efforts here?" Sen. Ron Johnson, a Republican from Wisconsin, said. "From my standpoint it's repairing the damage done by Obamacare," he said. "The biggest most notable damage is these skyrocketing premiums."

The fact is under Senate rules, there are still major questions about how many of the Obamacare regulations can actually be repealed through budget reconciliation, the process the Senate is using that allows them to pass a repeal bill with just 51 votes instead of 60.

Medicaid is another area, however, where finding consensus hasn't been easy. According to GOP aides, at Tuesday's Medicaid meeting, Majority Leader Mitch McConnell asked Republican Sens. Rob Portman of Ohio and Pat Toomey of Pennsylvania to discuss a Medicaid middle ground. By Thursday, it was already clear the lawmakers had run into a wall. Portman doesn't want the Senate bill to move any more to the right on Medicaid and made it clear throughout the meetings that he wanted to see a more gradual reduction in federal payments for Medicaid expansion rather than the abrupt cut-off in the House bill.

"Our concern is that we have to have a softer landing to ensure the states can pick up the slack and continue to provide coverage," Portman told reporters earlier in the week.

The working group, of course, is just the beginning of the process. In order to pass a repeal and replacement of Obamacare in the Senate, Republicans will need widespread buy-in.

For their part, Senate GOP leaders say that's exactly what they're in the process of securing. The Republican conference meets three times weekly when the chamber is in session, and McConnell has made clear that those meetings will be almost entirely about health care. It's a clear effort to ensure the entire conference is both looped in on the process and at the table to propose ideas or flag potential problems.

"The working group that counts is all 52 of us and we're having extensive meetings," McConnell told reporters last week. "We're having a discussion about the real issues. Everybody's at the table -- everybody."

It's a process leaders and members alike says will be -- has to be -- inclusive, and up to this point, the White House has deliberately given lawmakers the space to work through what is expected to be a lengthy and hard-fought process, aides say.

"I would tell people to take a breath and let the Senate do it's job," Cornyn told CNN last week. "We're going to get it done."

Any heavy-handed effort at this point would likely backfire given the clear splits that exist within the conference.

For example, there are 20 Republican members of the Senate who come from states that expanded Medicaid. Gutting the Medicaid program any more than the House bill proposes could significantly hamper the Senate bill's chances of passage. And, some moderates already have expressed other concerns about overhauling Obamacare regulations.

On Thursday, Sen. Bill Cassidy, a Republican from Louisiana who wrote his own Obamacare replacement bill with Sen. Susan Collins of Maine, took to the Senate floor to try to make the case that the Senate bill needs to better protect people with pre-existing conditions, something he called the "Kimmel test," a reference to the now-viral late-night TV moment in which ABC host Jimmy Kimmel grew emotional describing his infant child's health problems and the importance of affordable coverage for pre-existing conditions.

"We are going to protect those with pre-existing conditions, but we will do it by lowering premiums, and not by giving crumby coverage, but rather by having adequate coverage," Cassidy said.

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