President Donald Trump urged Republicans to “step up to the plate” for Tuesday’s crucial Senate vote on their bill eviscerating much of the Obama health care law. The stage was set for high drama, with Sen. John McCain returning to the Capitol to cast his first vote since being diagnosed with brain cancer.

No stranger to heroic episodes, the Navy pilot who persevered through five years of captivity during the Vietnam War announced through his office that he would be back in Washington for the critical roll call on beginning debate on the legislation. The 80-year-old has been at home in Arizona since he revealed last week that he’s undergoing treatment for brain cancer, but a statement said he “looks forward” to returning for work on health care and other legislation.

Senate Majority Leader Mitch McConnell, R-Ky., scheduled the initial health care vote for Tuesday. The Republican leadership expects McCain to support taking up the bill, and his mere presence could make it harder for wavering Republicans to cast a vote against even considering the bill.

Democrats uniformly oppose the effort to tear down Obama’s signature legislative achievement. Republicans control the chamber 52-48, meaning they can afford to lose just two Republicans with McCain around and only one in his absence. Vice President Mike Pence would cast a tie-breaking vote.

Trump kept up the pressure on GOP lawmakers, tweeting that “After 7 years of talking, we will soon see whether or not Republicans are willing to step up to the plate!” He added: “ObamaCare is torturing the American People. The Democrats have fooled the people long enough. Repeal or Repeal & Replace! I have pen in hand.”

At least a dozen GOP senators have openly said they oppose or criticized McConnell’s legislation, which he’s revised as he’s hunted Republican support. While it had long seemed headed toward defeat, Republicans Monday began showing glimmers of optimism.

“My mandate from the people of Kentucky is to vote yes, and I certainly intend to do so,” McConnell said Monday in what seemed an implicit reminder to his Republican colleagues that they’ve done the same.

As usual, Trump was blunter.

“Over and over again, they said, ‘Repeal and replace, repeal and replace.’ But they can now keep their promise,” Trump said in White House remarks Monday.

Senators and aides said talks were continuing that might win over enough Republicans to commence debate. The discussions were covering issues including potentially giving states more leeway to use federal funds to help people losing coverage under Medicaid, the health insurance program for the poor, disabled and nursing home patients.

Should Tuesday’s vote fail, it would be an unalloyed embarrassment for a party that finally gained control of the White House, Senate and House in January but still fell flat on its promise to uproot Obamacare. Republicans could try returning to the bill later this year if they somehow round up more support.

Should the initial motion win, that would prompt 20 hours of debate and countless amendments in a battle likely to last all week. Moderate and conservative Republicans would try reshaping the bill in their direction while Democrats would attempt to force GOP senators to cast difficult votes aimed at haunting them in re-election campaigns.

Even then, the measure’s ultimate fate still seemed iffy because of GOP divisions.

Obama’s law was enacted in 2010 over unanimous Republican opposition. Since then, its expansion of Medicaid and creation of federal insurance marketplaces has produced 20 million fewer uninsured people. It’s also provided protections that require insurers to provide robust coverage to all, cap consumers’ annual and lifetime expenditures and ensure that people with serious medical conditions pay the same premiums as the healthy.

The law has been unpopular with GOP voters and the party has launched numerous attempts to dismantle the statute. All until this year were mere aspirations because Obama vetoed every major one that reached him.

Ever since 2010, Republicans have been largely united on scuttling the statute but divided over how to replace it.

Those divides sharpened with Trump willing to sign legislation and estimates by the nonpartisan Congressional Budget Office that several GOP bills would cause more than 20 million people to become uninsured by 2026. Polls showing growing popularity for Obama’s law and abysmal approval ratings for the GOP effort haven’t helped.

The House approved its version of the bill in May after several setbacks. It’s similar to the Senate measure McConnell unveiled in June after writing it privately. But he’s also revised it in his hunt for GOP votes.

McConnell’s bill would abolish much of Obama’s law, eliminating its tax penalties on people not buying policies, cutting Medicaid, eliminating its tax boosts on medical companies and providing less generous health care subsidies for consumers.

Moderate Sen. Susan Collins, R-Maine, has remained opposed to beginning debate on any option McConnell has revealed so far. Conservative Sen. Rand Paul, R-Ky., said he would vote no unless leaders agreed to an early vote on simply repealing Obama’s statute and giving Congress two years to replace it.

Conservatives were seeking language letting insurers offer bare-bones policies with low premiums, which would be illegal under Obama’s law. Moderates from states whose low-income residents rely heavily on Medicaid were resisting the GOP bill’s cuts in that program.