Washington (CNN) The closely guarded Senate health care bill written entirely behind closed doors finally became public Thursday in a do-or-die moment for the Republican Party's winding efforts to repeal Obamacare.

The unveiling of the 142-page bill marks the first time that the majority of senators get a look at the plan to overhaul America's health care system. With Majority Leader Mitch McConnell pressing ahead for a vote next week, senators now only have a handful of days to decide whether to support or vote against the bill.

Four conservative Republican senators -- Rand Paul, Ted Cruz, Ron Johnson and Mike Lee -- said they opposed the current version. And key votes such as Sens. Dean Heller and Susan Collins have also withheld support.

"As currently drafted, this bill draft does not do nearly enough to lower premiums," Cruz said in a statement obtained by CNN. "That should be the central issue for Republicans -- repealing Obamacare and making health care more affordable. Because of this, I cannot support it as currently drafted, and I do not believe it has the votes to pass the Senate.

The bill would repeal Obamacare's individual mandate, drastically cut back federal support of Medicaid, and eliminate Obamacare's taxes on the wealthy, insurers and others.

President Donald Trump praised the bill Thursday -- though he acknowledged that changes were likely coming.

"It's going to be very good," Trump said at the White House. "A little negotiation but it's going to be very good."

With the exception of some key changes -- notably keeping Obamacare's subsidies to help people pay for individual coverage -- the bill is similar to the version of the House measure that passed last month which Trump has since called "mean" despite having a Rose Garden celebration with House Republicans.

Democrats blasted the bill, using Trump's "mean" judgment of the House bill.

"The Senate bill needed heart, the way this bill cuts health care is heartless," said Minority Leader Chuck Schumer. "This is a nasty bill and they're trying to cover it up with little things here and there."

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Can McConnell get the votes?

McConnell's decision to keep the details tightly under wraps until Thursday was intentional and aimed at winning over his colleagues out of the public spotlight, but the secretive process has infuriated Democrats -- and aggravated plenty of Republicans, too.

McConnell has very little room for error -- he can only lose two Republican votes and still pass the bill -- and GOP senators were not jumping to support it.

"Currently, for a variety of reasons, we are not ready to vote for this bill, but we are open to negotiation," Paul, Cruz, Johnson and Lee said in a joint statement. "There are provisions in this draft that represent an improvement to our current health care system, but it does not appear this draft as written will accomplish the most important promise that we made to Americans: to repeal Obamacare and lower their health care costs."

Sen. Orrin Hatch, R-Utah, told CNN that it would be "very difficult" for lawmakers to digest the bill in time for a vote next week.

Heller -- who will have a tough re-election in Nevada next year -- expressed "serious concerns" about the bill's impact on constituents who depend on Medicaid.

"If the bill is good for Nevada, I'll vote for it and if it's not -- I won't," Heller.

Still, others were more upbeat.

GOP Sen. John McCain, who has been openly critical of the lack of transparency in the crafting of the bill, said the proposal was better than Obamacare in "100 ways."

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What will CBO say?

The bill will have to undergo parliamentary scrutiny to ensure that it meets the strict requirements on what can or can't be included in a bill under the budget reconciliation process.

One report that will inform Senate Republicans as they decide whether to support the bill will be a score from the non-partisan Congressional Budget Office, which says it will release it early next week.

The CBO analysis will shed light on how much money the bill would cost and how many people would be covered. Senate Republicans hope to see better headlines from this CBO report than the one that the House GOP legislation received. CBO said the House bill would result in 23 million fewer people insured in 2026 than under Obamacare.

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Pre-existing conditions, Medicaid and other key issues

Pre-existing conditions: The Senate bill would require insurers to cover those with pre-existing conditions and ban them from basing premiums on consumers' health history.

But it would allow states to waive the federal mandate on what insurers must cover, known as the essential health benefits. This would allow insurers to offer less comprehensive policies, so those with pre-existing conditions may not have all of their treatments covered.

Last-minute House concessions to conservatives would have allowed states to opt out of several protections for those with pre-existing conditions.

Medicaid: This has been one of the central sticking points in the debate. The bill would continue the enhanced Medicaid expansion funding from Obamacare until 2021 and then phase it out over three years. This is a concession to moderates, who weren't pleased that the House version would end the enhanced support for new enrollees in 2020.

However, conservatives also get some of what they want when it comes to overhauling the entire Medicaid program. The Senate bill would keep the House plan to send a fixed amount of money to states each year based on enrollment or as a lump sum block grant. But it would shrink the program even more over time by pegging the annual growth rate of those funds to standard inflation, rather than the more generous medical inflation, starting in 2025. This would likely force states to cut enrollment, benefits or provider payments.

Premiums subsidies: The Senate bill would also largely maintain Obamacare's premium subsidies structure, but tighten the eligibility criteria starting in 2020. Fewer middle class folks would get help because only those earning up to 350% of the poverty level would qualify, rather than the 400% threshold contained in Obamacare. But it would also open up the subsidies to enrollees below the poverty level so those living in states that didn't expand Medicaid could get some assistance.

Senators opted to keep Obamacare's subsidies to prevent the funds from being used for abortions. The House bill called for creating tax credits based largely on age, but adding abortion restrictions to these credits could have run afoul of Senate rules governing the bill. Still, the similarities to Obamacare will likely infuriate conservatives such as Kentucky Senator Rand Paul, who decried the House version as "Obamacare Lite."

Planned Parenthood: As in the House bill, it would defund Planned Parenthood for one year.

Cost-sharing subsides: The bill would also aim to shore up the existing Obamacare market by allocating funds for the cost-sharing subsidies until 2019. This will placate insurers, who were distraught by Trump's refusal to commit to continue making these payments, leading many carriers to hike rates or drop out of the exchanges for 2018.