Key Republican senators came out against the Senate Republican health care plan on Thursday, and their opposition is enough to defeat the package before a vote.

Sens. Rand Paul, R-Ky., Ted Cruz, R-Texas, Mike Lee, R-Utah, and Ron Johnson, R-Wis., said they would not vote on the Senate Republican plan in its current form.

"Currently, for a variety of reasons, we are not ready to vote for this bill, but we are open to negotiation and obtaining more information before it is brought to the floor," the statement said. "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."

Paul told reporters on Capitol Hill Thursday that if members who support the bill know they don't have the votes needed, discussion would begin earlier.

"I didn't run on ObamaCare lite," Paul said. "I think we can do better than this --my hope is not to defeat the bill, but to make the bill better."

Paul added: "Now the discussions begin -- I think it could take longer than a week."

Cruz acknowledged that he had not yet had "the opportunity" to fully review the bill in its entirity, but said "there are components that give me encouragement and there are also components that are a cause for deep concern."

“I have been clear from day one that I want to get to yes,” Cruz told reporters on Capitol Hill Thursday. “Nobody has fought harder against ObamaCare in the Senate than I have, but we have to actually have legislation that fixes the underlying problem.”

Cruz said the current draft doesn’t do “nearly enough,” and would be a “disaster politically.” Cruz said that key components to “get everyone to yes” are lowering premiums, and giving the states flexibility.

Senate Republicans released a 142-page draft of their version of a "repeal and replace" health care plan on Thursday titled, “Better Care Reconciliation Act of 2017,” which eliminates a majority of ObamaCare provisions, already drawing backlash from Senate Democrats, and even some congressional Republicans.

The bill could go to a vote as early as next week, after the Congressional Budget Office reviews and gives a score to the new plan, but McConnell did not announce a specific timeline for consideration. The Congressional Budget Office expects to have a score for the draft “early next week.”

Senate Majority Leader Mitch McConnell, R-Ky., who rolled out the legislation, needs 50 votes to pass the bill to the House, with Vice President Mike Pence serving as the tie-breaking vote. But without the support of Paul, Cruz, Lee, and Johnson, passage of the bill in its current form will be nearly impossible, unless Republicans can manage to draw two Democratic votes, which is highly unlikely.

The bill repeals key components of ObamaCare, and manages to maintain some "crucial" conservative items congressional Republicans were looking for, like a cut to Planned Parenthood funding.

GOP SENATORS UNVEIL OBAMACARE OVERHAUL

But despite the early GOP-opposition, Sen. Chuck Grassley, R-Iowa, said he’s “glad the process is moving forward.”

“The Senate discussion draft is available for everyone to review,” Grassley said. “There will be a full debate before the Senate, with the ability for senators of both parties to offer amendments.”

But Democrats, as expected, are slamming the bill—and most are hanging on comments made by President Trump earlier this week, suggesting the House bill, called the American Health Care Act, was “mean.”

“The President said the Senate bill needs heart, the President says the House bill was mean,” Senate Minority Leader Chuck Schumer, D-N.Y., said on the Senate floor Thursday after the bill was rolled out. “The Senate version is meaner—the House bill is a wolf, but this bill is a wolf with sharper teeth -- it’s a wolf in sheep’s clothing.”

At the White House, the president remained consistent in his comment from earlier in the week, and said he hoped to get “something done” with “heart.”

“We’d love to have some Democratic support, but they’re obstructionist,” Trump said. “Hopefully we’ll get something done and it’ll be something with heart and very meaningful.”

Sen. Bernie Sanders, I-Vt., said the bill is “even worse than expected” and called it “by far the most harmful piece of legislation I have seen in my lifetime.”

“Our job now is to rally millions of Americans against this disastrous bill to make sure it does not pass the Senate,” Sanders said.

Despite Sanders’, and other Democrats’ criticisms, Sen. Lamar Alexander, R-Tenn., said the bill makes “no change” in current law when it comes to “protecting people with pre-existing conditions.”

McConnell said on the Senate floor Thursday that Democrats “made it clear early on” that they “did not want to work with us,” but Sen. Ron Wyden, D-Ore., said he had “never been asked.”

“It is not just a fiction, it is a gross fiction,” Wyden said.

Still, many members have yet to read the 142-page legislation in its entirety, with some Republicans hesitant to “forecast” votes, prior to reading the bill in full.

WHAT'S IN THE SENATE PROPOSAL: KEY PROVISIONS OF BETTER CARE RECONCILIATION ACT OF 2017

“I don’t know,” Sen. Luther Strange, R-Ala., told Fox News. “We’ve got a lot of work to do.”

Sen. Susan Collins, R-Maine, already has “a number of concerns,” according to her spokesperson, and plans to read the bill in full.

“She has a number of concerns and will be particularly interested in examining the forthcoming CBO analysis on the impact on insurance coverage, the effect on insurance premiums, and the changes in the Medicaid program,” Collins’ spokeswoman Annie Clark said.

On the other side of the Capitol, House Speaker Paul Ryan, R-Wis., said he had been briefed on the legislation, and is not going to “opine” the Senate’s process.

“I know how hard this process is from personal experience -- Last thing I want is to be disrespectful of the process ahead of them,” Ryan said. “We made a promise to repeal and replace -- eager for them to pass it but not going to opine on the details as they go along.”

Rep. Tom MacArthur, R-N.J., who authored a key amendment to the House’s plan, seemed satisfied with the Senate’s draft proposal.

“I am glad to see the Senate further improve the AHCA and put us one step closer,” MacArthur said.

McConnell said that when legislation comes to the floor, it will present Senate Democrats “another opportunity to do what’s right for the American people.”

Fox News' Chad Pergram, Mike Emanuel contributed to this report.