Neil Gorsuch. Photo: Justin Sullivan/Getty Images

Neil Gorsuch is almost certainly going to be the next Supreme Court justice, but the battle over how he gets there is going to be close. On Sunday, a third Democratic senator, Joe Donnelly of Indiana, announced his support for Gorsuch, but several hours later Democrat Jon Tester of Montana said he would vote against him. That means four more votes are needed to block Gorsuch, and eight Democrats remain undecided.

If Democrats manage to hold up Gorsuch’s nomination, Senate Majority Leader Mitch McConnell is expected to “go nuclear,” changing Senate rules so Gorsuch can be confirmed with a simple majority.

The ten Senate Democrats facing reelection in states President Trump won were supposed to be key to preventing a filibuster of Gorsuch’s nomination, and conservative groups spent $10 million on ads meant to pressure them into supporting him. But the campaign has had mixed results. The three Senate Democrats who oppose the filibuster – Donnelly, Heidi Heitkamp, and Joe Manchin — all hail from red states and are up for reelection next year. But while Trump carried Montana by 21 points, Senator Tester said he can’t back Gorsuch:

This is why I cannot support Judge Gorsuch's nomination to the Supreme Court: https://t.co/Q0nFBOJpCv pic.twitter.com/UiTvIHVrdY — Senator Jon Tester (@SenatorTester) April 3, 2017

The six other red-state Democrats — Claire McCaskill, Sherrod Brown, Bill Nelson, Bob Casey, Tammy Baldwin, and Debbie Stabenow — had already announced their opposition to Gorsuch.

The eight Democratic senators who are still undecided appear to have varied reasons for remaining noncommittal. Senators Ben Cardin and Patrick Leahy have said they’ll ultimately vote against Gorsuch, but they suggested they may join with Republicans on the procedural vote because they’re against filibustering Supreme Court nominees. Mark Warner and Chris Coons have expressed doubts about Gorsuch and his ability to overcome the filibuster, but haven’t explained where they stand. Michael Bennet, Dianne Feinstein, Bob Menendez, and Angus King (an independent who caucuses with Democrats) have offered few clues about how they’ll vote.

We should have a final answer by the end of the week. The Senate Judiciary Committee is set to refer Gorsuch to the full Senate on Monday. Republicans plan to have three days of formal debate, followed by a confirmation vote on Friday.

Sunday on Meet the Press, Senate Minority Leader Chuck Schumer predicted the filibuster of Gorsuch would hold, saying, “It’s highly, highly unlikely that he’ll get to 60.” He suggested that rather than changing Senate rules, Trump should nominate a less conservative judge. “Each side didn’t get their nominee,” Schumer said, referencing President Obama’s pick, Merrick Garland, who didn’t even get a hearing. “Let’s sit down and come together … and we will produce a mainstream nominee,” he said.

Unsurprisingly, McConnell did not seem open to that idea. “What I can tell you is Neil Gorsuch will be confirmed this week,” he said later on the show. “How that happens really depends on our Democratic friends.”