Washington (CNN) Senate Republicans voted Tuesday afternoon to advance to floor debate on their efforts to re-write health care policy, with Vice President Mike Pence breaking the tie.

But hours later, the Senate decisively rejected a Republican proposal to repeal-and-replace Obamacare, a sign of the chaos expected to envelop Capitol Hill as GOP leaders work to find a plan their conference can agree to.

Wednesday morning, floor debate on the legislation to overhaul the Affordable Care Act will continue, even though there aren't any guarantees the votes are there to eventually pass it -- and it's unclear what a final bill will look like.

But little may match the drama of Tuesday's vote on the motion to proceed, when Sen. John McCain returned from Arizona to applause from fellow senators to cast what would be a critical vote for the Republicans. Two GOP senators -- Susan Collins and Lisa Murkowski -- sided with all Democrats in opposition, meaning all remaining Republicans and Pence were necessary for the motion to pass.

Emotions were high all afternoon -- as the vote began, protesters in the Senate gallery shouted "kill the bill" and "shame, shame, shame!"

The vote came as Senate Majority Leader Mitch McConnell and President Donald Trump dared their fellow Republicans to block their seven-year campaign promise to repeal and replace Obamacare.

Senators late Tuesday cast their first vote on what could be dozens of amendments considered to it.

This first vote dealt with a measure that combined a previous Senate proposal known as the Better Care Reconciliation Act -- that was rejected by several Republican senators -- with $100 billion in extra money for people on Medicaid desired by moderate Republicans and a proposal from conservative Sen. Ted Cruz, R-Texas, to allow bare-bones health insurance plans.

Democrats moved successfully to kill the amendment, which was possible because it had not been officially scored by the Congressional Budget Office and therefore didn't meet the complicated reconciliation rules that the Senate is using to consider the bill.

Republicans needed 60 votes to keep the amendment alive. It died on a 43 to 57 vote.

The vote came after a Senate clerk was forced to read the text of the amendment aloud in the Senate chamber, all part of the delaying tactics Democrats employing to express their overall unhappiness with the bill.

On Wednesday, senators are expected to cast a vote on a "repeal-only" proposal. It too is expected to be defeated because many Republicans as well as all Democrats reject repealing without a replacement ready.

Drama before Tuesday's big vote

The vote was up in the air until the last moments, when several Republican holdouts announced their support, including Sens. Rand Paul, Dean Heller, Rob Portman and Shelley Moore Capito.

Trump, who has repeatedly said he's ready to sign any repeal legislation, celebrated the vote, which creates a path to give him the major congressional victory that's eluded the White House thus far.

"I'm very happy to announce that with zero of the Democrats' votes, the motion to proceed on health care has moved past and now we move forward toward truly great health care for the American people. We look forward to that. This was a big step," Trump said at a White House news conference.

"I want to thank Sen. John McCain," he added. "A very brave man. He made a tough trip to get here."

But while Trump was happy with the result, he also acknowledged there's a long road ahead for the legislation and criticized the two GOP senators who opposed the motion.

"We had two Republicans that went against us, which is very sad, I think," Trump said. "It's very, very sad -- for them. But I'm very, very happy with the result. I believe now we will, over the next week or two, come up with a plan that's going to be really, really wonderful for the American people."

Democrats are united against the bill, saying it would end health care coverage for millions of Americans.

"Anyone who thinks this is over is sadly mistaken," said Minority Leader Chuck Schumer, D-New York. "There are many, many Republicans who don't like this bill, who don't want to vote for it. They are under enormous pressure to vote for it. ... Anyone who voted to move to proceed and certainly anyone who votes to send this bill to conference is virtually, certainly, voting to kick millions off health care, to make it much harder to get coverage if you have a pre-existing condition, to slash Medicaid and give a huge amount of tax cuts to the rich."

Sen. Bernie Sanders Monday called the bill the "cruelest, most destructive and irresponsible piece of legislation ever brought to the United States Senate in the modern history of this country."

In a speech at the NAACP national convention, highlighted the possible effects of the bill's provisions, which include cutting Medicaid, defunding Planned Parenthood and roadblocks for those with pre-existing conditions.

JUST WATCHED McCain returns to Senate floor (full speech) Replay More Videos ... MUST WATCH McCain returns to Senate floor (full speech) 15:25

Paul, Heller back motion

McConnell won over key holdouts on the procedural vote, but those senators haven't said they will back the final measure.

Paul, a Kentucky Republican, said he would support the procedural motion to open debate on the health care bill, so long as leadership guarantees a vote on a full repeal of Obamacare.

"If this is indeed the plan, I will vote to proceed and I will vote for any all measures that are clean repeal," Paul tweeted. Such an amendment would be expected to fail, however.

Heller, who has complained that Obamacare repeal efforts could hurt Nevada residents dependent on Medicaid, nevertheless said he'd vote to move forward. Heller is facing a tough re-election campaign in Nevada next year.

"Obamacare isn't the answer, but doing nothing to try to solve the problems it has created isn't the answer either," Heller said in a statement. "If the final product isn't improved for the state of Nevada, then I will not vote for it; if it is improved, I will support it."

Republican leaders Tuesday worked thread any needle they can to appease other holdouts.

"The only goal is to get onto the bill. Nothing happens until we do, so that's the only goal," a Republican aide said.

"These are the moments legislatively when you get creative. We're getting creative."

JUST WATCHED Trump: Senate GOP can end Obamacare nightmare Replay More Videos ... MUST WATCH Trump: Senate GOP can end Obamacare nightmare 02:28

This story has been updated.