President Trump’s selection of Brett M. Kavanaugh as his choice for the next Supreme Court justice sets into motion an intense battle over the future of the court — and all eyes are now on the Senate, where Republicans hold a slim 51-to-49 majority. With Sen. John McCain (R-Ariz.) away from Capitol Hill as he undergoes treatment for brain cancer, Kavanaugh’s fortunes could hinge on a single vote. Here are two groups of senators who will play a pivotal role in the confirmation process, along with their reactions to Monday night’s news.

Republican Sens. Susan Collins of Maine, Lisa Murkowski of Alaska and Rand Paul of Kentucky:

Collins and Murkowski, two GOP moderates who support abortion rights, will likely bear the brunt of Democratic pressure to oppose Kavanaugh’s confirmation. Murkowski has called Roe v. Wade a “significant factor” in her decision, though not the only one. Collins — the senator who appears most likely to cross party lines — has previously voted for President Obama’s two Supreme Court picks.

The libertarian-leaning Paul, meanwhile, adds another layer of unpredictability. He has reportedly voiced reservations about Kavanaugh in private and has previously had no qualms about sharply opposing his party, even to the point of triggering a short-lived government shutdown earlier this year. All three emphasized in their statements on Monday night that they look forward to thoroughly vetting Kavanaugh.

Collins : “Judge Kavanaugh has impressive credentials and extensive experience, having served more than a decade on the D.C. Circuit Court of Appeals. I will conduct a careful, thorough vetting of the President’s nominee to the Supreme Court, as I have done with the five previous Supreme Court Justices whom I have considered. I look forward to Judge Kavanaugh’s public hearing before the Senate Judiciary Committee and to questioning him in a meeting in my office.”

Murkowski : “This evening the President nominated Judge Brett Kavanaugh to serve as an Associate Justice of the Supreme Court. While I have not met Judge Kavanaugh, I look forward to sitting down for a personal meeting with him. I intend to review Judge Kavanaugh’s decisions on the bench and writings off the bench, and pay careful attention to his responses to questions posed by my colleagues on the Senate Judiciary Committee. The American Bar Association’s Standing Committee on the Judiciary will also review Judge Kavanaugh’s qualifications prior to these hearings and issue a rating. I intend to carefully consider that rating, the information obtained through personal meetings, my own review of Judge Kavanaugh’s qualifications and record, and the views of Alaskans in determining whether or not to support him. My standard for reviewing Supreme Court nominees remains rigorous and exacting.”

Paul : “I look forward to the upcoming hearings, reviewing the record, and meeting personally with Judge Kavanaugh, with an open mind.”

Democratic Sens. Joe Donnelly of Indiana, Heidi Heitkamp of North Dakota, Joe Manchin III of West Virginia, Doug Jones of Alabama and Claire McCaskill of Missouri:

These senators from states that Trump won by wide margins in 2016 are in an unenviable position, as they will likely face a barrage of criticism however they choose to cast their vote.

Under the greatest pressure are Donnelly, Heitkamp and Manchin, a trio of red-state Democrats who are up for reelection and who last year voted to confirm Trump’s first Supreme Court nominee, Neil M. Gorsuch. All three met with Trump at the White House last month to discuss the latest Supreme Court opening.

Jones, while not up for reelection until 2020, is still likely to face an uphill battle and has so far declined to say how he plans to vote. He, like the three senators mentioned above, turned down an invitation from the White House to attend Monday night’s announcement in the East Room.

And McCaskill, who is up for reelection and voted against Gorsuch last year, is viewed as a likely “no” vote this time as well, although it’s worth keeping an eye on her.

Like their Republican counterparts, the Democratic senators on this list also refrained from issuing strong opinions about Kavanaugh on Monday night, instead emphasizing the need for careful deliberation.

Donnelly : “As I have said, part of my job as Senator includes thoroughly considering judicial nominations, including to the Supreme Court. I will take the same approach as I have previously for a Supreme Court vacancy. Following the president’s announcement, I will carefully review and consider the record and qualifications of Judge Brett Kavanaugh.”

Heitkamp : “An exhaustive and fair process took place for Justice Gorsuch, who I supported, and it should and must take place again now.”

Manchin : “As the Senator from West Virginia, I have a constitutional obligation to advise and consent on a nominee to fill Supreme Court vacancies and I take that responsibility seriously. Just as I did when Merrick Garland and Neil Gorsuch were nominated, I will evaluate Judge Kavanaugh’s record, legal qualifications, judicial philosophy and particularly, his views on healthcare. The Supreme Court will ultimately decide if nearly 800,000 West Virginians with pre-existing conditions will lose their healthcare. This decision will directly impact almost 40% of my state, so I’m very interested in his position on protecting West Virginians with pre-existing conditions. As I have always said, I believe the Senate should hold committee hearings; Senators should meet with him, we should debate his qualifications on the Senate floor and cast whatever vote we believe he deserves. I look forward to meeting with Judge Kavanaugh, examining his rulings and making a determination of whether to provide my consent.”

Jones : “Tonight’s announcement is only a first step. A thorough vetting of Judge Kavanaugh’s body of work will be critical for the Senate to fulfill its shared responsibility — which I take very seriously. I will be diligent in measuring the record and in undertaking an independent review.”

McCaskill : “I look forward to thoroughly examining Judge Kavanaugh’s record in the coming weeks as the Senate considers his nomination to replace Justice Kennedy.”

For more details on Kavanaugh’s record during his 12 years on the bench in Washington, click here.

Amber Phillips contributed to this report.