"If that is the plan, I will vote to proceed to have this vote," the senator wrote on Twitter. Paul also said that if the simple repeal doesn’t pass, "I’ve also been been told we will vote on whatever version of CLEAN repeal we can pass."

Republican Arizona Senator John McCain, who was diagnosed this month with brain cancer, returned to Washington Tuesday for the vote. His presence could provide an emotional lift to GOP lawmakers, whom President Donald Trump urged to seize the moment.

For a Senate leader like McConnell who takes pride in engineering the outcomes he wants, it’s an uncharacteristic gamble. A close vote could put even more pressure on holdouts to back GOP leaders. But a defeat by a wide margin could doom the repeal effort, possibly for good.

McConnell pleaded with his colleagues Tuesday to open the debate.

“We can do better than Obamacare, and we have a responsibility to the American people to do that,” he said on the Senate floor. “Today’s vote to begin debate is the first step. We should take it.”

Senator Roy Blunt of Missouri, a member of the leadership team, said Tuesday he can’t say whether McConnell has the votes to get the health debate started.

“As you know, Senator McConnell is pretty closely held,” Blunt said.

Trump tried to apply maximum pressure on senators ahead of the vote to pass some kind of repeal measure.

‘Obamacare Nightmare’

“Any senator who votes against starting debate is telling America that you are fine with the Obamacare nightmare,” he said in a televised statement Monday from the White House.

The president, who criticized McCain during the 2016 campaign for being captured during the Vietnam War, tweeted Tuesday it was “so great” and “brave” that the “American hero” was returning to vote, and told Republicans he has a “pen in hand” to sign an Obamacare repeal -- or repeal-and-replace -- measure if they “are willing to step up to the plate!”

John Cornyn, the No. 2 Senate Republican, said the aim is for Republicans to pass something and go to conference with the House.

“Everything’s on the table. It’s whatever we can get out of the Senate and get to a conference,” he said when asked about possibility of a stripped-down repeal measure that would eliminate the mandates and the medical device tax.

With Republicans holding a 52-48 margin in the Senate, Republicans can only lose two Republicans and still pass a repeal bill. Vice President Mike Pence could cast a tie-breaking vote.

Susan Collins of Maine said she will vote against beginning debate on any of the measures currently on offer.

QuickTake Q&A: This Unelected Official Holds Sway on Health Care

Senator John Thune, the No. 3 Senate Republican, said the McConnell bill is still being tweaked to deal with parliamentary rulings and potentially to appeal to holdout senators like Rob Portman of Ohio.

But Paul said he doesn’t know if any of his amendments have been sent to CBO to see if they qualify under a fast-track mechanism that would allow the health bill to pass with 50 votes instead of 60.

Hard Work

“Leadership is going to have to work a lot harder to give an opportunity for conservatives to want to get on this bill,” he said.

Thune said a majority of Republicans want to hold a vote even if they don’t have the votes to start debate. “However it turns out, we’re ready to move.”

“I’m still hoping we’re going to get there,” he said.

GOP leaders are making a pitch to senators that they will each get a chance to vote on their preferred bill and that the final measure will be put together by leadership at the end of the debate. McConnell said the measures that would get votes include the 2015 Obamacare-repeal bill with a two-year delay that was vetoed by President Barack Obama. Trump would sign such a bill, the majority leader said.

But it’s been difficult for McConnell to win over moderate holdouts without alienating conservative Republicans who have raised objections amid unified Democratic opposition.

Outside groups have also ramped up the pressure, with conservative organizations pressuring Republicans to deliver on seven years of promises to repeal Obamacare.

Seniors’ Lobby

AARP, the powerful lobby group that represents older Americans, urged the Senate to reject the measure and said it would communicate to members in key states how their senators voted.

“We will report to all 38 million AARP members how their Senators vote, via ads, our print publications, social media and more,” the group said Monday night on Twitter.

Pence is expected to be available Tuesday at the Senate in case his vote is needed to break a tie, Health and Human Services Secretary Tom Price told reporters. Trump’s budget office issued a statement urging senators to agree to begin debate.

Several Republicans have already said they oppose repealing Obamacare without a replacement, including Collins.

‘Still Fluid’

Senator Pat Roberts of Kansas, a GOP member of the health committee, said senators are discussing revisions to McConnell’s plan to replace Obamacare, which collapsed for lack of support last week. The majority leader then said he would seek to bring a simple repeal of Obamacare to the floor early this week, but that proposal also fell apart amid opposition from Collins and others.

“It’s still fluid,” said Roberts, who added that he wants to support whatever plan emerges because he opposes leaving Obamacare in place.

Cornyn said Monday the GOP won’t give up on replacing Obamacare if the Senate can’t pass it this week. “If for some reason we aren’t able to muster the votes tomorrow, which I’m increasingly optimistic we will, it’s not the end of it," he said.

Roberts said his main concern is the effect of spending cuts on rural hospitals that get Medicaid funds. “Under the current system, they’re just not going to be able to make it," Roberts said. "We’ve just got to figure out a way to make that work better.”

He said he was in touch over the weekend with Seema Verma, the Trump administration’s head of Medicare and Medicaid, and that her proposal to make up some funding with non-Medicaid money has potential.

It will be hard to get people who have taken hard stands against McConnell’s plan or portions of it to change their positions, Roberts said.

‘Awfully Difficult’

“It’s awfully difficult when people climb the tree and get out on a limb and say, ‘I’m going to vote no,”’ the Kansas senator said. “For them to skinny back down that tree, that’s tough. And they have to have some very good reasons as to why that’s the case.”

Efforts to resurrect McConnell’s Obamacare replacement suffered a further blow on Friday when the Senate parliamentarian issued a preliminary finding that key parts of the proposal don’t qualify for the fast-track procedure being used by the GOP. Those parts would require 60 votes rather than the simple majority the GOP seeks to use, Parliamentarian Elizabeth MacDonough said.

Among them are provisions that would defund Planned Parenthood for a year, prevent tax credits from being used to buy insurance policies that cover abortion, and encourage people to have continuous insurance by barring those without coverage for at least two months from buying new insurance for half a year.

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