July 25, 2017 9:29 AM EDT

After numerous failed attempts to fulfill a seven-year promise to repeal-and-replace the Affordable Care Act, Senate Republicans are making yet another bid to pass a replacement bill–without a final product ready.

The Senate will vote on Tuesday to begin debate on the health care bill that passed the House in May, Majority Leader Mitch McConnell announced on Monday. But Senate leadership has yet to reach a consensus on any bill, leaving some lawmakers in doubt as to whether the abrupt procedural vote will lead to the passage of an Obamacare overhaul.

It is unclear if McConnell even has enough votes to pass a motion to begin debate. With only 52 Republicans in the Senate, he has a small window to work with. Republican Sen. Susan Collins of Maine is expected to vote no on the motion to proceed. That means that McConnell can likely afford to lose just two other votes.

The majority leader did, however, receive a bit of good news on Monday. Republican Sen. John McCain, who was diagnosed with brain cancer last week and considered a long shot to return to Washington anytime soon, announced he will be back on Capitol Hill in time for the vote Tuesday.

“Many of us have waited literally years for this moment to finally arrive, and at long last, it has,” McConnell said on the Senate floor about Tuesday’s vote.

But if the motion passes, there is no telling what will replace the House bill. Senators will have the opportunity to propose countless amendments to the bill, which can include everything from a minor tweak to a complete overhaul.

“Everybody will get a vote on everything they want to vote on,” Republican Sen. John Cornyn said. “What we’re trying to do is convince everybody that if they’d like to get a vote on their amendment, then they need to vote to proceed to the House bill.”

President Trump has turned up the heat on Senate Republicans in recent days, pressuring them to come to an agreement on health care reform. On Monday, the president tweeted that the vote is Republicans’ “last chance to do the right thing.”

“Any senator who votes against starting debate is telling America that you are fine with the Obamacare nightmare, which is what it is,” Trump said at a White House press conference Monday in which he railed against his predecessor’s signature achievement, calling it “death.”

McConnell and Senate leadership have proposed multiple drafts of a health care replacement bill in recent weeks but have been unable to corral enough support for any bill. The latest ACA replacement draft, which hit a roadblock last week, would leave 22 million without insurance by 2026, according to the nonpartisan Congressional Budget Office.

After that bill failed, McConnell proposed passing a 2015 Senate bill–which was vetoed by President Barack Obama–that would repeal the ACA now and give lawmakers time to come up with a replacement in the future. McConnell’s Plan B was also reviewed by the Congressional Budget Office back in 2015. The agency said that a repeal-now, replace-later bill would cause 18 million to lose insurance by next year and 32 million by 2026. The bill failed only a few hours after McConnell floated the idea.

Both bills will be considered if a motion to proceed passes.

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Write to Jack Brewster at jack.brewster@time.com.

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