Republicans are closer than they have ever been to sending an ObamaCare repeal bill to the president’s desk.

But it’s far from a done deal.

The House has voted 56 times to repeal all or part of ObamaCare, but those Republican-led efforts have died in the Senate.

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Now that the upper chamber is under Republican control, the party has a chance to score a significant — if only symbolic — victory on Thursday.

President Obama would veto the bill, but clearing it through Congress would be a rare legislative win for the GOP on the controversial healthcare law.

With a couple of defections expected, it’s unclear whether Senate Republicans have the necessary 51 votes. Thursday’s dramatic roll call is expected to go down to the wire.

Republicans can only afford three GOP defections, if all senators vote.

Republican leaders are still not 100 percent certain how some senators will vote. Conservative Sen. Ted Cruz Rafael (Ted) Edward CruzTrump argues full Supreme Court needed to settle potential election disputes Press: Notorious RBG vs Notorious GOP The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy MORE’s (R-Texas) office and centrist Sen. Susan Collins Susan Margaret CollinsSenate GOP aims to confirm Trump court pick by Oct. 29: report The Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Senate GOP sees early Supreme Court vote as political booster shot MORE (R-Maine) declined to say Wednesday which way they are leaning.

Collins has raised concerns about language in the bill that would eliminate federal funds for Planned Parenthood.

Cruz, a presidential candidate, has called for the complete repeal of ObamaCare, but the current bill is more targeted. It’s also unclear how other White House hopefuls, such as Sens. Marco Rubio Marco Antonio RubioOvernight Defense: Pentagon redirects pandemic funding to defense contractors | US planning for full Afghanistan withdrawal by May | Anti-Trump GOP group puts ads in military papers Democrats step up hardball tactics as Supreme Court fight heats up Press: Notorious RBG vs Notorious GOP MORE (R-Fla.) and Rand Paul Randal (Rand) Howard PaulSecond GOP senator to quarantine after exposure to coronavirus GOP senator to quarantine after coronavirus exposure The Hill's Morning Report - Sponsored by National Industries for the Blind - Trump seeks to flip 'Rage' narrative; Dems block COVID-19 bill MORE (R-Ky.), will vote.

“You’re never totally 100 percent sure, but I think the checks all look good and the concerns of a number of members have been addressed,” said Senate Republican Conference Chairman John Thune John Randolph ThuneSenate GOP sees early Supreme Court vote as political booster shot Romney backs pre-election Supreme Court vote, paving way for McConnell, Trump Senate GOP faces pivotal moment on pick for Supreme Court MORE (S.D.), the third-ranking member of the leadership.

The Senate bill actually goes significantly further than a version the House passed earlier this year.

It would repeal the law’s health insurance exchanges, subsidies and tax increases as well as an expansion of Medicaid that has been adopted by 30 states.

The legislation would also unwind risk-adjustment programs used to reimburse insurance companies that spend more on sick patients than they collect in premiums and would repeal the Prevention and Public Health Fund.

Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellPelosi: Trump hurrying to fill SCOTUS seat so he can repeal ObamaCare Senate GOP aims to confirm Trump court pick by Oct. 29: report Trump argues full Supreme Court needed to settle potential election disputes MORE (R-Ky.) needs 51 votes to pass the repeal package under a special budgetary process known as reconciliation that circumvents the 60-vote hurdle usually required for controversial bills.

He has ramped up pressure on colleagues in recent weeks to vote yes.

McConnell’s message is simple: Failure is not an option.

“This is America’s chance to turn the page and write a new and more hopeful beginning,” he said on the Senate floor Wednesday. “This is our chance to work toward a healthier and more prosperous future with true reform that moves beyond the failures of a broken law.”

“We made a promise to [voters] that if they gave us the majority last November we would have this vote and we would place this squarely in front of the president,” Senate Republican Whip John Cornyn John CornynThe Hill's Campaign Report: GOP set to ask SCOTUS to limit mail-in voting Liberal super PAC launches ads targeting vulnerable GOP senators over SCOTUS fight Senate GOP faces pivotal moment on pick for Supreme Court MORE (Texas) said.

Senate aides expect votes on eight to 15 amendments before final passage, which is likely to take place in the late afternoon or early evening. A group of Democrats is hoping to fly out of Washington late Thursday to attend climate change meetings in Paris on Friday.

Republican centrists are not happy with the Planned Parenthood measure.

“I want that provision to be dropped,” Collins said, adding that her vote on final passage may “depend on what happens on the amendment.”

“I don’t understand why the Planned Parenthood provisions were included in the bill in the first place,” she said. “Why the complete defunding of all Planned Parenthood clinics, which would result in the closure of virtually all of them, was included in this bill was a mystery to me.”

Sen. Mark Kirk Mark Steven KirkLiberal veterans group urges Biden to name Duckworth VP On the Trail: Senate GOP hopefuls tie themselves to Trump Biden campaign releases video to explain 'what really happened in Ukraine' MORE (R-Ill.), a centrist who faces a challenging reelection race, has also raised concerns about the Planned Parenthood language.

Kirk’s office declined to say Wednesday how the senator would vote on the final package.

Collins, Kirk and Sen. Lisa Murkowski Lisa Ann MurkowskiSenate GOP aims to confirm Trump court pick by Oct. 29: report Senate GOP sees early Supreme Court vote as political booster shot Pence defends Trump's 'obligation' to nominate new Supreme Court justice MORE (R-Alaska) have co-sponsored an amendment to strike the Planned Parenthood provision.

But that amendment is expected to fall short. If it does, Murkowski might choose to oppose the final bill.

Meanwhile, some conservatives are adamant that all of ObamaCare should be scrapped.

The Senate parliamentarian, Elizabeth MacDonough, has advised that the entire law cannot be repealed at once using the special simple-majority procedure, which requires provisions to directly affect the federal budget.

As a result, some aspects of the healthcare law, such as allowing children to stay on a parent’s health plan until age 26 and barring insurance companies from discriminating on the basis of pre-existing conditions, have been left out of the repeal package.

Cruz could attempt to go around the parliamentarian by calling for a vote to overturn the ruling of the Senate’s presiding chairman, who almost always makes those rulings based on the advice of the parliamentarian.

The Texas senator could argue that Republicans who have campaigned on repealing ObamaCare “root and branch” should pass a one-sentence repeal over MacDonough’s objections. This controversial tactic would be akin to the “nuclear option” that Democrats triggered in 2013 to exempt most judicial and executive branch nominees from filibusters.

A senior GOP aide said leaders are prepared for such a parliamentary power play in case Cruz tries it.

Cruz, Rubio and Sen. Mike Lee Michael (Mike) Shumway LeeMcConnell shores up GOP support for coronavirus package McConnell tries to unify GOP Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE (R-Utah) issued a statement in October pledging to oppose the House-passed repeal bill for not going far enough.

To address their concerns, McConnell and other Senate GOP leaders dramatically broadened the scope of the repeal package by additionally targeting the exchanges, subsidies, tax increases and risk adjustment mechanisms.

Leaders emphasized to colleagues this week their package would save around $400 billion over 10 years, compared with the $78 billion saved by the House package.

On Wednesday evening, Lee announced on the Senate floor that he will vote yes.

The House package will be altered during the vote-a-rama expected to begin early Thursday afternoon.

Sen. Bernie Sanders Bernie SandersButtigieg stands in as Pence for Harris's debate practice Bernie Sanders warns of 'nightmare scenario' if Trump refuses election results Harris joins women's voter mobilization event also featuring Pelosi, Gloria Steinem, Jane Fonda MORE (I-Vt.), a presidential candidate, is co-sponsoring an amendment with Sens. John McCain John Sidney McCainCindy McCain endorses Biden: He's only candidate 'who stands up for our values' Biden says Cindy McCain will endorse him Biden's six best bets in 2016 Trump states MORE (R-Ariz.) and Amy Klobuchar Amy KlobucharSocial media platforms put muscle into National Voter Registration Day Battle lines drawn on precedent in Supreme Court fight Sunday shows - Ruth Bader Ginsburg's death dominates MORE (D-Minn.) to allow for the re-importation of prescription drugs from Canada.

Jordain Carney contributed.