Senate Majority Leader Mitch McConnell. Bill Pugliano/Getty Images The Senate narrowly voted on Tuesday to open debate on the Republican effort to overhaul healthcare, kicking off a furious voting process after tumultuous arguments within the GOP.

A procedural vote to begin debate on the House's healthcare bill passed, 51-50, as Vice President Mike Pence cast the tiebreaking vote. It came amid the dramatic return of Sen. John McCain, who cast a crucial vote in favor of the legislation, a week after announcing he had brain cancer.

Even with this step, it is unclear whether Republicans will have the votes to eventually repeal and replace the Affordable Care Act, the healthcare law known as Obamacare.

Every Democrat voted against the motion on Tuesday, as well as Republican Sens. Susan Collins and Lisa Murkowski. GOP leadership could not have afforded another defection.

Several Republican members who were on the fence about the motion voted for the measure after significant pressure from Majority Leader Mitch McConnell and the White House. Sen. Ron Johnson came to the floor and talked privately with McConnell before finally casting a "yes" vote.

The Senate will now begin 20 hours of debate on the healthcare bill, equally divided between Democrats and Republicans.

To get enough Republican senators on board with the motion to proceed, McConnell most likely promised to bring to a vote multiple versions of amendments, including the Obamacare Repeal Reconciliation Act, which would repeal the law, and the Better Care Reconciliation Act, which would repeal and replace it.

GOP members say McConnell is most likely assuming both of those measures will fail and will then begin a so-called skinny repeal process — a series of amendments that would repeal certain parts of the ACA.

If those passed within the shell of the House bill, Republicans from both sides of Congress would come together in a conference committee to draft a compromise.

"I applaud the Senate for taking a giant step to end the Obamacare nightmare," President Donald Trump said in a statement. "As this vote shows, inaction is not an option, and now the legislative process can move forward as intended to produce a bill that lowers costs and increases options for all Americans. The Senate must now pass a bill and get it to my desk so we can finally end the Obamacare disaster once and for all."

Here's a rundown of what could happen from here: