Senate Minority Leader Mitch McConnell on Thursday announced he will not vote for Ketanji Brown Jackson‘s nomination to the Supreme Court, citing her responses this week to questions about “court packing.”

“I went into the Senate process with an open mind, but after studying the nominee’s record and watching her performance this week, I cannot and will not support Judge Jackson for a lifetime appointment to the Supreme Court,” McConnell, R-Ky, said on the Senate floor.

McConnell suggested in his remarks that he thought Jackson would be an activist judge, and faulted her for not taking a position on court packing — adding additional justices to the nine member Supreme Court.

“Judge Jackson refuses to reject the fringe position that Democrats should try to pack the Supreme Court,” McConnell said, adding that the question should have been “an easy softball” for her, “but it wasn’t.”

Jackson noted during her confirmation hearing that Justice Amy Coney Barrett, a conservative judge who McConnell championed for the Supreme Court in 2020, sidestepped a similar question during her hearing, saying she wouldn’t “opine” on the issue.

McConnell also noted that liberal justices like Stephen Breyer and the late Ruth Bader Ginsburg “had no problem denouncing this unpopular view and defending their institution.” The two justices made those remarks after they were on the Supreme Court.

He added that Jackson “seemingly actually tipped her hand” during her testimony this week. “She said she would be ‘thrilled to be one of however many.’ However many,” McConnell said.

“Nothing we saw this week convinced me that President Biden’s or Judge Jackson’s far-left fan club had misjudged her. I will vote against this nominee on the senate floor,” he said.

The Senate Judiciary Committee is expected to vote on Jackson’s nomination April 4, setting up a likely vote in the full Senate later that month. No Democrats have indicated they would oppose her.

McConnell was not expected to back President Joe Biden‘s historic pick — he voted against Jackson’s nomination to the U.S. Court of Appeals for the D.C. Circuit last year — but Thursday’s announcement could open the floodgates for other GOP senators to follow suit and potentially set up a party-line vote for Jackson, who would be the first Black woman to serve on the Supreme Court.

Jackson was confirmed last year to her current post by a vote of 53-44, with support from just three Republicans: Sens. Susan Collins of Maine, Lisa Murkowski of Alaska and Lindsey Graham of South Carolina.

Graham, however, was openly antagonistic toward Jackson during her confirmation hearings this week, criticizing her sentencings in child pornography cases.

Graham has yet to reveal how he plans to vote on Jackson’s nomination. He told NBC News Thursday, “I’m inclined to vote for nominees,” but suggested he might hold Jackson to different standard for the Supreme Court than he did for the federal appeals court. “I thought she was qualified to be on the circuit court. This is a different game,” he said.

Asked if that meant he would vote against her, Graham said, “Now just stay tuned.”

Frank Thorp V and Garrett Haake contributed.