President Trump and Senate Majority Leader Mitch McConnell, R-Ky., want to move swiftly to confirm the justice to succeed retiring Supreme Court Justice Anthony Kennedy before the court reconvenes on October 1.

With Arizona Republican Sen. John McCain's continued absence due to ongoing brain cancer treatment, McConnell has a functional 50-vote majority and little room for error in what is shaping up to be a partisan fight over the ideological makeup of the court for the next generation. With only 99 senators currently voting, the nominee can be approved by a 50-49 margin. In the event of a 50-50 tie, Vice President Pence would cast the deciding vote.

There is no nominee yet, but Trump indicated on Friday he will likely pick from a short list of roughly five candidates, all of which have bona fides among conservatives and align ideologically with Justice Neil Gorsuch. Gorsuch cleared the Senate — only after McConnell pushed through a rules change to end the filibuster on Supreme Court nominees and lower the threshold for confirmation from 60 to a simple majority — with 54 votes .

Senate Democrats are calling to delay the vote until after the midterm elections, but McConnell has rejected their call and there is little Democrats can do to ultimately delay a vote.

Already the confirmation process is becoming a debate about the future of abortion rights in America and whether the nominee would uphold the landmark 1973 Roe v. Wade decision and subsequent challenges that have upheld a woman's right to abortion access. The future of Kennedy's seat has been a moment abortion rights opponents and supporters alike have been anticipating for years because Kennedy historically sided with the liberals on the court in favor of protecting abortion rights.

It's no secret in Washington, D.C., who the critical senators will be in the months ahead. Trump invited all five to the White House for a private meeting the day after Kennedy announced his retirement.

Two moderate Republican women

Few senators are as familiar with — and as cool at handling — the hot seat than Sens. Susan Collins of Maine and Lisa Murkowski of Alaska. The swing-vote senators, along with McCain, were the trio who derailed the GOP's 2017 effort to repeal most of President Barack Obama's Affordable Care Act.

They are also the only two Republican women who support abortion rights — with some caveats — and they could ultimately be the deciding votes on the Supreme Court nomination if all 49 members of the Senate Democratic caucus (including two independents) band together and oppose the nominee as a unified block.

Collins has a more reliable record in favor of abortion rights, and boasts a 70-percent vote rating in 2018 from Planned Parenthood's political arm. Collins wasted no time following Kennedy's announcement to reiterate that she believes Roe v. Wade is "settled law," but a spokeswoman told the Portland Press Herald that Collins "does not apply ideological litmus tests to nominees."

Collins is inclined to support nominees — she has voted to confirm every Supreme Court pick that has come up for a Senate vote during her time in the Senate — but none may be as consequential as Kennedy's replacement. "No matter how I vote there are going to be people who are furious at me," Collins told POLITICO .

Murkowski isn't rated as favorably among abortion rights groups, she has a 58-percent vote rating in 2018 from Planned Parenthood, but arguably there is no one in the Senate more independent than the Alaska Republican, and prouder of her reputation among women in her state.

Murkowski lost her 2010 GOP primary, but ultimately won re-election with a historic write-in campaign. The strength of her victory was fueled by support among Alaska women, which has become part of Murkowski's brand. She has also been a reliable defender of federal funding for Planned Parenthood , which provides health care services to thousands of Alaskans.

In a statement , Murkowski noted her standards for the Supreme Court are "extremely high" and that she will cast an "independent vote" when the eventual nominee comes before the Senate. Neither senator is known for telegraphing how they will cast their votes until right before the vote is called, so the spotlight will likely be on them in the months ahead.

One factor that eases the immediate political pressure on both senators: Collins is not up for re-election until 2020; Murkowski in 2022.

Three red-state Democrats

There are ten Democratic senators up for re-election in 2018 in states that Trump won in 2016. When it comes to the Supreme Court fight, that list is quickly culled to just three for one reason: they are the only Democrats who voted to confirm Gorsuch in 2017 — Indiana Sen. Joe Donnelly, North Dakota Sen. Heidi Heitkamp and West Virginia Sen. Joe Manchin.

Each of the three has a complex, frenemy-style relationship with the president, and each is trying to find the right political balance of working with a president most of their constituents strongly support, and opposing him where it matters most to their own voters.

For Republicans' part, they need to balance actively campaigning against the trio in 2018, while courting their votes for the Supreme Court nominee. If either or both Collins and Murkowski end up opposing the nominee, support from some combination of this Democratic trio will be necessary to achieve a simple majority in the Senate.

President Trump initially bashed Heitkamp at a rally in North Dakota this week in which he urged voters to support her GOP opponent, Rep. Kevin Cramer. "Heidi will vote 'no' for any pick we make for the Supreme Court," Trump said. However, he invited her, Donnelly and Manchin to the White House the next day to discuss the nomination process.

"Political speeches are just that, but the next day, I'm ready to get to work," Heitkamp said in a statement following a private meeting with the president. "I stressed the importance of nominating someone to the Supreme Court who is pragmatic, fair, compassionate, committed to justice, and above politics."

Heitkamp broadly supports abortion rights, but North Dakota is one of the most restrictive states in the nation when it comes to abortion access. Red-state Democrats are generally loathe to make their campaigns about social issues, and Heitkamp has preferred to work with the Trump administration on economic and energy grounds.

Unlike Heitkamp, Donnelly and Manchin are Democrats who generally oppose abortion rights and are endorsed by Democrats for Life , the "pro-life voice of the Democratic Party." The two men have also, at times, had warm relations with the president. Donnelly has traveled with Trump on Air Force One, and appeared alongside the president at a recent bill signing ceremony at the White House.

Manchin might be Trump's closest ally across the aisle — the president even considered him for a Cabinet job — and Manchin left open the possibility of supporting Trump for re-election in 2020.

Like Collins and Murkowski, these Democrats are unlikely to reveal how they will vote until the nomination comes to the Senate floor. McConnell told Fox News that Republicans believe some combination of Democratic support is possible. "We're hoping there will be some Democratic support," he said, "We're not assuming this is just going to be a straight party-line vote. I think there will be some Democrats who find the nominee attractive."

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