John McCain came to Donald Trump's rescue to help push through a key Senate vote to abolish Obamacare, in a dramatic return to Congress following surgery for brain cancer.
The vote - which allows the Senate to begin debate on health care reform legislation - was a narrow victory for the U.S. President, who had spent weeks cajoling, strong-arming and warning Republicans to get on board with his effort to overhaul Obamacare.
McCain, who announced last week he is suffering from brain cancer, cast a critical vote for the measure, leaving senators evenly split and forcing Vice President Mike Pence to break the tie for a 51-50 final count.
All 48 Democrats and independents voted against, along with Republicans Susan Collins and Lisa Murkowski.
McCain received a standing ovation from his colleagues as he entered the chamber, having made the trip from his home state of Arizona, where he was convalescing.
Despite the vote just scraping through in Trump’s favour, he was delighted.
"This was a big step," he said shortly after the vote at a press conference in the White House Rose Garden, calling Obamacare a "disaster for the American people".
In a fuller statement released by the White House after the vote, Trump said: “I applaud the Senate for taking a giant step to end the Obamacare nightmare.
“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."
Senators will now launch into long hours of debate, with Republican conservatives and moderates divided over how to proceed.
The first votes on changes to the bill could come as early as Tuesday night, a Republican leadership aide said.
The question then becomes what can get over the finish line. Lawmakers have begun speaking about a "skinny" repeal that would dismantle only parts of the Affordable Care Act, but it is not yet clear whether the plan will gain traction this week.
"We can do better than Obamacare," Senate Majority Leader Mitch McConnell said. "Today's vote to begin debate is the first step."
Trump has repeatedly grilled fellow Republicans for not following through on their - and his - campaign pledge to repeal and replace Obamacare.
On the Democratic side, senators urged cooperation - and restraint.
"I can't believe this process and the hard and calculated rhetoric we see," Democratic Senator Joe Manchin of West Virginia said Tuesday.
"The Affordable Care Act is not a perfect piece of legislation. It needs repair. We both agree to that. Then we need to fix it."
Forecasts by the non-partisan Congressional Budget Office on various health reform bills have predicted that millions of Americans would lose health care if the measures become law.
In the case of a bill that repeals Obamacare and provides no replacement, 32 million more people would be uninsured by 2026 as compared to current law, CBO forecast.