But McConnell left some wiggle room — even he doesn’t say he’s got the votes.

If successful, Graham and Cassidy would accomplish what McConnell couldn’t: Make good on the GOP’s pledge to undo Obamacare and transform Medicaid from an open-ended entitlement into a capped program. Critics say the result would be draconian cuts that would throw millions off of their health coverage and endanger the most vulnerable Americans.

The men behind the plan could not be more different: Cassidy, a physician and first-term senator, is cerebral and academic. Graham, a longtime Senate veteran, is blunt, chatty and quotable. Santorum, a conservative activist and frequent TV talk show guest, likes to reminisce about his days authoring the rare successful rollback of an entitlement — the 1996 welfare reform bill signed by former President Bill Clinton. He compares the welfare bill with the health care effort in that both rely on block grants to the states.

Santorum and Cassidy worked on the policy in the Graham-Cassidy bill. Graham played the salesman, courting the White House and GOP governors — and complained jokingly but often about getting bogged down in policy minutiae.

After Cassidy went into the details of actuarial values at a press conference last week, Graham quipped that he “had to listen to this crap for two months.”

“If you want to have an interesting evening, do not go to dinner with Ron Johnson and Bill Cassidy,” Graham warned on the Senate floor last week, referring to the Wisconsin Republican who joined their bill as a sponsor. “They are wonderful people, but they know numbers and they love to talk about details and how systems work.”

While the idea of health care block grants has circulated for years in conservative policy circles, Graham credits Santorum with pushing it as the key to replace Obamacare.

“Rick said, ‘Why don’t you just do a block grant like we did with welfare reform,’” Graham said. “When you look at it, it’s such an elegant, fair, common-sense solution to a complicated problem.”

Santorum first floated the concept to House conservatives in late March, just days after Speaker Paul Ryan pulled his chamber’s repeal bill from the House floor.

The House Freedom Caucus had banded together to block what they deemed “Obamacare lite,” so Santorum began meeting with Chairman Mark Meadows (R-N.C.) and member Raul Labrador (R-Idaho) to make his pitch.

During one meeting early on, Santorum name-dropped Graham. He said he believed his old Senate colleague was also open to the idea of block grants and could help sell it — bridging the divide between moderates and conservatives.

“Santorum said, ‘You’ll never guess who might be somewhat supportive of this in the Senate and willing to work with you guys on it,’” Meadows recalled in a Wednesday interview. “And that’s when he mentioned Lindsey Graham.”

Meadows passed on Santorum’s idea then, in favor of a more robust Obamacare repeal amendment that would eventually pass the House.

But Santorum kept pushing his brainchild — particularly when it looked as though the Senate would fail to clear its own health care bill.

Over the summer, Santorum, Graham and Meadows talked about the block-grant plan as a last-ditch backup — what Meadows now jokes was “Option C or Option D” on the repeal menu.

“Certainly we wouldn’t be here today had it not been for the initial conversations that Rick Santorum initiated,” Meadows said.

Eventually, they brought in Cassidy, who has long pushed for block grants and who knows the ins and outs of health care policy as none of them did. Cassidy’s initial plan, with Sen. Susan Collins, to let states enact their own health care policies, including Obamacare, had faltered after it was deemed too moderate by conservatives.

By the end of July, when the Senate repeal bill failed and most Republicans prepared to move on to tax reform, Graham, Cassidy and Santorum kept working.

The trio was adamant about having something ready to go before the Sept. 30 deadline to pass a Senate bill with a simple majority. Sens. Dean Heller (R-Nev.) and Ron Johnson (R-Wis.) joined the bill shortly before it was released.

“I thought that could solve the problem, sort of break the logjam here,” Santorum said of his own involvement. “So I fleshed out a bill for [Graham’s] staff, and it’s sort of been the basis for what happened.”

Graham focused on selling the bill in the Senate, while Santorum reached out to Meadows to ensure the proposal would get the support of House conservatives if it passed the Senate.’

Graham also reached out to the White House, keeping President Donald Trump and his advisers in the loop in case the effort developed traction. “They’re on speed dial,” Cassidy said of Graham and Trump. “As much as they kind of back and forth, they’re just like my daughter and her best friend.”

The White House puts its thumb on the scale earlier this week when it made clear Trump wouldn’t sign a bipartisan bill being written by Lamar Alexander and Patty Murray to try to stabilize Obamacare markets. That gave momentum to Graham-Cassidy.

Now it’s down to the whipping operation — nailing down 50 of the 52 GOP senators, with Rand Paul already a strong no.

Santorum, who is covered by an Obamacare insurance plan today, jokingly refers to himself as a “glorified staffer,” but it’s clear he wishes he could cast a vote.

If that were the case, he said, “we wouldn’t have to be scrambling for votes right now.”

Burgess Everett contributed to this report.