In the looming battle resulting from President Donald Trump’s pick of Judge Brett Kavanaugh to the US Supreme Court, there’s a big question: Can Senate Minority Leader Chuck Schumer keep his Democratic caucus united to vote against the new nominee?

Republicans don’t need Democratic votes to confirm Kavanaugh, but they will matter if any Republican senators defect. (The Republican senators to watch here are Sens. Susan Collins of Maine and Lisa Murkowski of Alaska.)

The most closely watched Democratic votes will be those of three red-state Democrats who voted for Neil Gorsuch’s Supreme Court confirmation in 2017: Sens. Joe Manchin of West Virginia, Heidi Heitkamp of North Dakota, and Joe Donnelly of Indiana.

All three are facing tough reelection battles in states where Trump won overwhelmingly in 2016, so they’re eager to prove they are working with the president and Senate Republicans. But a vote for a Trump Supreme Court pick risks infuriating the Democratic base in all three states and alienating left-leaning voters. Progressive groups are already planning to lobby moderate Republicans and Democrats aggressively on this issue.

Based on their public statements after Trump’s pick was announced, Heitkamp, Manchin, and Donnelly are keeping their thoughts close to the vest, saying they want to meet Trump’s nominee before making a decision.

We know that Trump is already trying to pressure them: All three were invited to watch Monday’s Supreme Court announcement at the White House but either declined or were unable to make it. (Sen. Dianne Feinstein, a Democrat from California and ranking member of the Senate Judiciary Committee was also invited.)

In a statement to reporters, Donnelly said he first wanted to meet the nominee in a setting where he could ask questions about the person’s “experience and perspectives.”

NEW: @SenDonnelly was invited to WH for SCOTUS but said no. “While I appreciate the invitation frm the White House to attend this evening’s announcement, I declined so that I can meet first with the nominee in a setting where we can discuss his or her experience and perspectives” — Seung Min Kim (@seungminkim) July 9, 2018

Manchin, in a tweet, said something similar. He mentioned his interest in talking about health care — an issue he cares a lot about and one he has clashed with Trump on in the past. Health care is expected to be one of the hottest issues during Senate confirmation hearings, given the numerous legal challenges to the Affordable Care Act.

I appreciate the President inviting me to attend tonight's announcement at the WH. I look forward to meeting the nominee in a setting where we can discuss his or her experience, judicial philosophy & perspective on access to healthcare for WVians with pre-existing conditions. — Senator Joe Manchin (@Sen_JoeManchin) July 9, 2018

Heitkamp echoed Donnelly and Manchin in her statement, saying she plans to fully vet Kavanaugh before making a decision of whether to vote for him.

“I have no doubt that many members of Congress and outside groups will announce how they stand on the nominee before doing their due diligence and instead just take a partisan stance — but that isn’t how I work,” Heitkamp wrote.

My statement on the nomination of Judge Kavanaugh to serve on the Supreme Court: pic.twitter.com/ia1yOICT9P — Sen. Heidi Heitkamp (@SenatorHeitkamp) July 10, 2018

It’s worth pointing out that last year Heitkamp, Donnelly, and Manchin stuck with the Democratic caucus on crucial votes, including those on steep GOP tax cuts and the failed Republican attempt to repeal the Affordable Care Act. This vote could be even more crucial, as a Supreme Court justice will make decisions on a wide array of issues.

A few more red-state senators are also facing tough 2018 reelection campaigns, but because they voted against Gorsuch they’re not being watched as closely as Heitkamp, Manchin, and Donnelly.

As Vox’s Andrew Prokop wrote: