(CNN) The window is quickly closing if Senate Republicans want to vote on a health care bill before the July 4 recess.

But if the GOP leaders are on the cusp of a vote, most senators aren't in the loop. Republican leaders continue to be under fire -- even from their own members -- for their tightly guarded process to repealing Obamacare.

It's being kept under wraps by design. Majority Leader Mitch McConnell needs to be as close to 50 votes as possible before he unveils his legislation. Reveal it too soon and criticism from outside conservative groups, independent reviews and Democrats could have the bill unravel before it hits the floor.

That means the critical lawmakers are also holding back.

"Until I see the bill and the (Congressional Budget Office) assessment of the bill, I'm not going to feel comfortable taking a position," said Sen. Susan Collins, a Republican from Maine.

Democrats are also weighing their options this week on how to slow the GOP's health care efforts. Sen. Bernie Sanders said he is "in favor" of Democrats using parliamentary tactics that could essentially bring the Senate to a halt.

"I am in favor," Sanders told CNN's Jake Tapper on "State of the Union" Sunday. "I am in favor of the American people and members of Congress doing everything that we can to defeat that horrific piece of legislation that will hurt tens and tens of millions of people in our country."

One Senate aide says Democrats' current plan is to hold the floor until midnight and members will use the time to tell constituent stories about the Affordable Care Act.

Another twist: Tuesday's special congressional election in Georgia. A win for Democrat Jon Ossoff could be seen as a stark warning to President Donald Trump and the GOP Obamacare repeal efforts.

Against that background, McConnell's task this week is two-fold: finish a bill and convince enough people to back it.

Here are the players who will decide the fate of health care in the Senate this week.

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Ohio Republican Sen. Rob Portman

While the GOP has railed against Obamacare for years, there's one pillar of the health care law that plenty of Republican lawmakers now say is pivotal for their constituents: Medicaid expansion.

The House health care bill proposes gutting the program, effectively ending enhanced federal funding for Medicaid in 2020.

But Senate Republicans who hail from states that expanded Medicaid under Obamacare say that would cut off vital resources for some of their most vulnerable constituents much too abruptly.

Portman, a member of the Senate working group on the bill, has led the effort to convince leadership to accept a seven-year "glide path" -- a longer transition period in which Medicaid expansion state governors can figure out an alternative to the program. It's unclear what concessions leadership will ultimately make on the Medicaid front.

One sticking point in these deliberations is what will happen to patients who receive opioid treatment under expanded Medicaid. Senators like Portman are calling for more resources to be provided to governors so that opioid treatment funding doesn't end up on the chopping block.

Nevada Republican Sen. Dean Heller

Up for re-election in 2018 in a state Hillary Clinton won, Heller is perhaps one of the most vulnerable Republicans in this health care debate. Heller also comes from a state that thanks to expanded Medicaid has seen its uninsured rate drop from 23 percent to 12 percent.

The senator has been fighting alongside Portman to more slowly phase out federal money for Medicaid expansion. But Heller is facing a bit more pressure from back home. His Republican Gov. Brian Sandoval told the Nevada Independent this week he would prefer the expansion didn't go away at all.

That's not going to happen in the Senate where non-expansion Republicans have argued that Medicaid-expansion states shouldn't be allowed to keep more federal money.

Texas Republican Sen. Ted Cruz

Cruz is trying a new role in the debate over health care: negotiator.

Rather than sticking to the firebrand, leadership-agitating strategy that defined his early years in the Senate, Cruz -- and those who have been working with him-- insist he is working constructively behind the scenes to get to 'yes' on health care.

But that doesn't change the fact that Cruz is still one of the Senate's most conservative members who has said that he wants to ensure that the Senate health care bill actually lowers premiums.

Like many conservatives, Cruz believes that in order to bring down the cost of health insurance, lawmakers need to repeal as many of the Obamacare-era regulations as possible. He also has advocated to repeal Obamacare taxes as soon as possible.

A twist: Cruz is up for re-election in 2018. And a bad position for Cruz would be to on the opposite side of Trump who has said he likes the direction the Senate bill is moving.

Alaska Republican Sen. Lisa Murkowski

Murkowski has been frank about her frustration with how the Senate is crafting their health care bill. She was invited to the White House to meet with the President last week on health care, but told reporters after the meeting that she had no idea if she was having an impact in the process because "I have no idea if we even have a bill."

"I mean I learn more from you all," she said to reporters.

Murkowski is independent-minded and fiercely loyal to Alaska, which has some of the most expensive insurance premiums in the country. Murkowski has said she wants to make sure that the Senate bill's tax credits are more generous for those living in rural places like Alaska than the House bill's were. She also has been critical of defunding Planned Parenthood, an item that will likely be included if McConnell needs conservative support for his bill.

Murkowski's not an easy get, but if leadership is amendable to her wishes, it could give an indication that the bill is moving in a more moderate direction.

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Maine Republican Sen. Susan Collins

Collins isn't a member of the Senate "working group," but the Maine Republican is pivotal player in the health care debate -- and a critical vote for leadership to win over.

The moderate senator already released an "Obamacare replacement" bill this year along with Louisiana Sen. Bill Cassidy, aimed at giving states more power to determine their own health care policy. One option for states under this legislation: keep Obamacare if they like it.

Collins has made clear that she sees serious problems with the legislation that House Republicans passed last month, and is a rare proponent of working with Democrats on a health care plan. She voted against Republicans' Obamacare repeal bill in 2015. She has also been very clear with her Senate leaders that if they want to create a high-risk pool like the House bill did, they need to allocate more money for it.

She has argued that her state's high risk pool is a good model, but that it is an example of how much money is needed to ensure the program's success. She presented on her state's high risk pool to colleagues during a Senate lunch and spoke about it during the White House meeting with Trump.

Along with Murkowski, she supports preserving federal funding for Planned Parenthood as well. Although she says it is just one of many factors that will have an effect on the way she votes.

"There are a lot of important issues," Collins said last week when asked about it.

Republican Sens. Mike Lee of Utah and Rand Paul of Kentucky

Two of the most conservative members in the Senate are going to be major players in the race to count health care votes. Paul is already talking like he's leaning against anything that remotely looks like the House bill. There is, of course, no bill yet, but Paul criticized the House bill for allocating money for tax credits, which he says sound like another entitlement program. If anything, many expect the Senate bill will be more generous with those credits.

"What I'm telling them is if they get to an impasse, come talk to me because I am more than willing to vote for a partial repeal if I can't get complete repeal, but I'm not willing to vote for new Republican entitlement programs," Paul said.

Lee, has advocated, that more -- not fewer -- Obamacare regulations should be repealed but so far it looks like the Senate is leaning toward repealing fewer of the regulations than the House bill.