The Senate Judiciary Committee launched confirmation hearings for Supreme Court nominee Brett Kavanaugh on Tuesday, kicking off what is expected to be a bitterly partisan gauntlet as Democrats vow to scrutinize his lengthy record as an appellate judge and lawyer in the Bush administration.

In excerpts of his opening statement released by the White House Tuesday morning, Kavanaugh vowed to be an objective "pro-law judge."

"A good judge must be an umpire—a neutral and impartial arbiter who favors no litigant or policy," he plans to say. "I don’t decide cases based on personal or policy preferences. I am not a pro-plaintiff or pro-defendant judge. I am not a pro-prosecution or pro-defense judge. I am a pro-law judge. ... If confirmed to the Court, I would be part of a Team of Nine, committed to deciding cases according to the Constitution and laws of the United States."

Kavanaugh's elevation from the D.C. Circuit Court of Appeals to replace retired Justice Anthony Kennedy would mark a generational rightward shift on the Supreme Court, raising the stakes beyond those of last year's nomination of Neil Gorsuch and leading Democrats to ratchet up their rhetoric.

Last month, Sen. Cory Booker, D-N.J., accused anyone who supports Kavanaugh of being "complicit in evil." After ex-Trump lawyer Michael Cohen’s guilty plea – which was used by Democrats to push for Kavanaugh delays – Sen. Mazie Hirono, D-Hawaii, even nixed a one-on-one meeting with the nominee, claiming Trump had picked him "purposely ... to protect, as we say in Hawaii, his own okole" from possible criminal charges. Some Democrats, including Sen. Bob Casey, D-Pa., had rejected Trump's selection before they even knew who it was, predicting the nomination process would be a "corrupt bargain with the far Right, big corporations, and Washington special interests."

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But Kavanaugh steadily has gathered support from legal circles, former colleagues and Republican lawmakers. Senate Judiciary Committee Chairman Chuck Grassley, R-Iowa, called him "perhaps the most qualified person ever nominated to the Supreme Court."

The judge's nomination, though, will ultimately succeed or fail depending on a handful of swing-vote senators, including vulnerable red-state Democrats and moderate pro-choice Republicans who have all said that they would withhold judgment on the nominee.

Republicans command a narrow 50-49 Senate majority, which would return to 51-49 once a Republican successor to the late Sen. John McCain is appointed. Republicans have little margin for error, though Vice President Pence can break a tie.

Who are the senators to watch?

Among the key votes on the Democratic side are Indiana's Joe Donnelly, West Virginia's Joe Manchin and North Dakota's Heidi Heitkamp. All three voted to confirm Gorsuch to the Supreme Court last year, and all are up for re-election in November in states that went for Trump in the 2016 presidential election. Each has also met with Kavanaugh on Capitol Hill, and has promised to carefully weigh the upcoming hearings before making a final call.

Alabama Democratic Sen. Doug Jones, who recently won a special election and will be up for election in 2020, is also considered a potential yes vote on the nominee. But he recently said he wanted to delay Kavanaugh's confirmation hearings, citing the "cloud" of suspicion around Trump and his desire to see more documents from his time in the Bush White House. Jones claimed his view was shared by “everybody else around here on the Democratic side of the aisle" -- but some Democrats, including Manchin, dismissed those last-minute concerns, saying there was no basis to delay the hearings.

Even before former Trump attorney Cohen pleaded guilty last month to several federal charges, Democrats had already called for Kavanaugh's hearings to be postponed until after the November midterms, in retaliation for Senate Republicans' decision to deny a vote on then-President Barack Obama's Supreme Court nominee Merrick Garland in 2016.

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Meanwhile, outside groups have been pressuring moderate Republican Sens. Lisa Murkowski of Alaska and Susan Collins of Maine. Both have promised to remain independent and carefully consider the results of Kavanaugh's confirmation hearings, but have given some clues on their leanings.

Last month, Murkowski vowed to take a "similar, if not identical … approach I took for Justices Gorsuch, Kagan, Sotomayor, Alito and Roberts" in vetting the nomination. Murkowski voted to confirm Kavanaugh to a seat on the influential D.C. Circuit Court of Appeals in 2006.

And Collins, who also voted to confirm Kavanaugh in 2006, acknowledged shortly after Trump nominated him to the Supreme Court that he has "impressive credentials and extensive experience, having served more than a decade on the D.C. Circuit Court of Appeals."

Notably, Collins has rejected calls from Democrats to delay Kavanaugh's confirmation hearings, saying there was "no basis" for the move. After meeting with Kavanaugh on Capitol Hill, Collins said Kavanaugh had reassured her that Roe v. Wade, the landmark Supreme Court case that established a constitutional right to an abortion, was "settled law."

NARAL Pro-Choice America and the American Civil Liberties Union (ACLU) have spent hundreds of thousands of dollars targeting Murkowski and Collins specifically, Politico reported, in an effort to sway them against Kavanaugh.

Another influential liberal group opposing Kavanaugh, the Alliance for Justice (AFJ), told Fox News that both Collins and Murkowski would jeopardize their reputations by failing to vote down his confirmation.

"For someone like Collins or Murkowski, their legacy is really on the line here," AFJ Legal Director Dan Goldberg said. "Whatever votes they had in the past to protect women, to protect health care, would long be forgotten -- they would have to own every decision Brett Kavanaugh makes."

Goldberg added that Kavanaugh's national poll numbers are "consistent with Robert Bork and Harriet Miers" when they were under consideration for Supreme Court posts they ultimately didn't receive. A Fox News poll last month showed voters evenly divided on Kavanaugh.

After his sit-down with Kavanaugh on Capitol Hill last month, Senate Minority Leader Chuck Schumer, D-N.Y., also made his case to Murkowski and Collins.

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"He would not give me any reassurance that he believed Roe or [Planned Parenthood v. Casey] were correctly decided or should be left alone," Schumer claimed. "That should send shivers down the spine of any American who believes in reproductive freedom."

Sen. Booker echoed that line of attack after his own meeting with Kavanaugh, telling reporters, "A lot of folks were wondering that he might not overturn Roe v. Wade. ... He confirmed with me that that door was still wide open."

Still, Schumer, who also implied Kavanaugh was lying about the details of his time in the Bush White House, acknowledged that Kavanaugh had told Collins that Roe was settled law.

"I understand that the judge told other members today that he considered Roe v. Wade settled law," Schumer said, before adding, "He did not say that to me."

Kavanaugh's paper trail -- asset or liability?

Kavanaugh has left one of the longest paper trails of any recent Supreme Court nominee, having served for more than a decade on the D.C. Circuit Court of Appeals and, before that, for five years as a lawyer in the White House Counsel's office in the George W. Bush administration. Kavanaugh also worked for independent counsel Ken Starr for three years during the probe that led to the impeachment of former President Bill Clinton.

In looking at Kavanaugh's jurisprudence, Democrats will likely focus on Kavanaugh's decisions in cases like Priests for Life v. HHS, in which Kavanaugh wrote a dissent arguing that ObamaCare's contraceptive coverage requirements put undue burdens on some religious beliefs.

Both parties are also likely to grill Kavanaugh on his 2011 dissent in an ObamaCare case, Sevensky v. Holder, which Republican critics have claimed effectively provided the Supreme Court with a roadmap to uphold the law's contentious individual mandate provision. In his dissent, Kavanaugh wrote that only a "minor tweak" to the text of ObamaCare -- which required individuals to purchase health coverage or pay a monetary cost -- would bring it within the ambit of Congress' established power under the Constitution's Taxing Clause.

Chief Justice John Roberts would later provide the swing vote to uphold to ObamaCare's individual mandate by citing Congress' power under the Taxing Clause, instead of adopting the Obama administration's arguments that the law was justified broadly under the Constitution's expansive authority to generally regulate interstate commerce.

But others, including a former Kavanuagh law clerk, called that interpretation "nonsense" and argued that Kavanaugh, in fact, was outlining why Congress' Taxing Clause could not save ObamaCare from unconstitutionality.

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Democrats are also expected to question Kavanaugh about Garza v. Hargan, a recent case in which Kavanaugh dissented from a ruling that the Trump administration should permit an illegal immigrant in federal custody to have an abortion. Kavanaugh's dissent managed to anger both sides of the abortion debate, because while Kavanaugh did not endorse the immigrant's right to an abortion, his dissent also did not specifically deny her that right in all cases.

In the wake of several high-profile school shootings, Democrats may further zero in on Kavanaugh's position on gun rights. Kavanaugh dissented in the landmark Heller case when it was before the D.C. Circuit, arguing that a D.C. ordinance unconstitutionally infringed on residents' right to own semi-automatic weapons by requiring them to keep them unloaded and unassembled, or bound by a trigger lock.

Additionally, liberal groups have highlighted Kavanaugh's record on the environment, saying that he has overzealously struck down Environmental Protection Agency regulations. In a case last year, Mexichem Flour v. EPA, Kavanaugh wrote a majority opinion that struck down a 2015 EPA rule regulating hydrofluorocarbons, which analysts say led to substantially increased greenhouse gasses. Kavanaugh reviewed the text of the Clean Air Act and the legislative history before writing that the EPA's rule had exceeded the agency's statutory authority under the Clean Air Act -- although he sounded a note of regret in the process.

"However much we might sympathize or agree with EPA's policy objectives, EPA may act only within the boundaries of its statutory authority," Kavanaugh wrote. "Here, EPA exceeded that authority."

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But Supreme Court nominees are typically unwilling to offer much insight into their legal philosophies during confirmation hearings, which carries a major political risk and could prejudice future cases before the Supreme Court. There was also a greater potential for Democrats to score points by questioning Kavanaugh on his record as a Bush administration lawyer and adviser to Kenneth Starr, especially given that his writings in those capacities were less guarded than a typical judicial opinion.

During the Clinton investigation, for example, Kavanaugh unloaded on Clinton, telling Starr that the president should be impeached, citing his "revolting" behavior in the Oval Office and "sheer number of wrongful acts." But since his time in the Bush White House, Kavanaugh has argued that presidents should not have to endure lengthy probes during their time in office, saying in 2009 that indicting sitting presidents would "ill serve the public interest," especially in times of financial or national security crisis.

He wrote in an article that year: “[T]he nation certainly would have been better off if President Clinton could have focused on Osama bin Laden without being distracted by the Paula Jones sexual harassment case and its criminal investigation offshoots.”

That language has alarmed top Democrats, who have voiced concerns that Kavanaugh would vote to shoot down a subpoena or even indictment of President Trump if one were filed by Special Counsel Robert Mueller or other federal prosecutors.

Meanwhile, Democratic concerns that Kavanaugh may have misled the Senate Judiciary Committee during his 2006 confirmation hearings for his D.C. Circuit post have fizzled in recent weeks. A document dump last month from Kavanaugh's time in the Bush White House suggested that he had, in fact, offered legal advice on attorney-client privilege issues surrounding terror detainees, even though he said under oath that he had no involvement in "rules governing the detention of combatants." The White House has maintained Kavanaugh's statements were truthful, and the controversy died down.

Nevertheless, Goldberg, the AFJ legal director, said he anticipates that Democrats will hammer the issue during this week's hearings.

"There are certainly questions about his candor and veracity in front of the Senate Judiciary Committee when he was first confirmed --- issues that I know Sen. [Patrick] Leahy will press him on in the hearing," Goldberg told Fox News, referring to the long-time Vermont Democratic senator who serves on the Judiciary Committee. Leahy has opposed Kavanaugh dating back to his 2003 nomination to the D.C. Circuit, saying he had "failed to demonstrate his capacity for independence." Democrats stalled Kavanaugh's appellate court nomination until 2006.

In recent days, Democrats, including Leahy, have cried foul that the Kavanaugh paper trail is actually not long enough, saying they have been denied access to all the documents they need to vet his nomination. Schumer has threatened to sue the National Archives, which is handling their requests for documents from Kavanaugh's public service. He has also sharply criticized the procedure for the ongoing document production, saying it's inappropriate that a Republican lawyer is vetting all documents before their release.

Despite Kavanaugh's voluminous record -- and the all-out contentious rhetoric surrounding it -- Senate Majority Whip John Cornyn, R-Texas, has said Republicans hope to have Kavanaugh confirmed by a floor vote by early October, when the next Supreme Court term begins.

Fox News' Adam Shaw contributed to this report.