Eighty-one-year-old Shirley Abrahamson has been chief justice of the Wisconsin Supreme Court for 18 years, but that tenure looks like it’s about to come to an abrupt end.

A state constitutional amendment, passed Tuesday in the state Senate 17-14 along strict party lines, will allow the court’s seven justices to vote on a chief justice, undoing a 126-year-old tradition that grants the post to the longest-serving justice on the bench. If the bill passes the state Assembly and wins voter approval April 7, the next chief justice, selected by the court’s conservative majority, will almost certainly be Justice Pat Roggensack.

Justice Roggensack may not yet be chief, but she has already led the Wisconsin Supreme Court through an era of remarkable procedural change. The court’s justices are elected and run campaigns, complete with TV ads, one of which earned Justice Michael Gableman an ethics charge in 2009. Most important, the justices can establish political committees to accept donations on their behalf from individuals, corporations, and what remains of Wisconsin’s unions.

In 2010, Justice Roggensack and the three other conservatives on the bench ruled that, “a judge shall not be required to recuse himself or herself in a proceeding based solely on any endorsement or the judge’s campaign committee’s receipt of a lawful campaign contribution, including a campaign contribution from an individual or entity involved in the proceeding.” The ruling, which was met with an angry dissent from Chief Justice Abrahamson and the other liberal justices, dictates that a justice can rule on a case—or at least cannot be forced to recuse himself—even if one of the parties in the case contributed to that justice’s campaign committee.

What might appear to be a fairly straightforward model for corruption of the judiciary is, according to Justice Roggensack, completely legitimate. Channeling the U.S. Supreme Court’s Justice Anthony Kennedy, the conservatives ruled that such an arrangement does not undermine public confidence in the court, nor does it promote the appearance of corruption. Instead, they maintained that if justices were forced to recuse themselves, groups could force them off cases by donating to their campaigns or running ads on their behalf. The conservative justices also made the remarkable argument that a Supreme Court justice’s recusal “alters the number of justices reviewing a case as well as the composition of the court.”

Justice Roggensack and her Supreme allies’ dealings with conflicts of interest do not end there. The court agreed last year to hear a case resulting from the much-publicized “John Doe” investigation into possible violations of campaign finance law by Wisconsin Gov. Scott Walker’s campaign during the recall elections of 2011 and 2012. That investigation has faced considerable opposition from the governor’s office, as might be expected. But it also has run into sustained legal challenges from outside political groups, resulting in numerous delays and moratoriums on the investigation.

Among those groups are Wisconsin Club for Growth and Wisconsin Manufacturers and Commerce. Both are named among the outside political groups with which the Walker campaign is alleged to have coordinated. Both ran so-called issue ads in support of Walker that disparaged his opponents. And, along with another group called Citizens for a Strong America, both have contributed more than $8 million to elect the four conservative justices on the Wisconsin Supreme Court.

The 2010 ruling helped those justices build a platform to justify their participation in the John Doe case. Scot Ross, a liberal activist and head of One Wisconsin Now, called the decision a “get-out-of-jail-free card” for powerful interests that invest in Supreme Court races. “The vast majority of spending to elect these four justices was done by these entities,” Ross told the Wisconsin State Journal.

In 2011, “$3 out of every $4” spent to elect Justice David Prosser, a member of the court’s conservative wing, came from outside groups. Wisconsin Manufacturers and Commerce spent $1.1 million on Justice Prosser’s behalf, while Club for Growth dished out $520,000. He is now expected to rule impartially in a case alleging that both of those groups broke the law.

At the top of the 2010 decision to reform the recusal procedures, there is an explanation of how the case came to be. “On September 30, 2008, and October 16, 2009, the Wisconsin Realtors Association, Inc. and Wisconsin Manufacturers and Commerce, respectively, petitioned this court to amend the Code of Judicial Conduct.” Wisconsin Manufacturers and Commerce sought the rule change after another justice, Annette Ziegler, came under fire for hearing a case pushed by the group after it had spent $2.2 million to get her elected. The ruling makes clear in Section 2 that justices are free to rule on cases involving parties that spent independently on the justices’ behalf in addition to those donating directly to candidate committees.

The state Assembly is expected to take up and pass the constitutional amendment on chief justice selection Thursday, in time for it to make the April 7 election ballot as a referendum. Spring elections are notorious for their low turnout—19 percent voted in April 2013—and the measure is expected to succeed. The court will likely have a new chief justice just in time for its ruling on the John Doe case, expected to be issued this summer.

For their part, the Republicans in the state legislature insist the amendment is not partisan. “This is not about the current chief justice,” said the bill’s sponsor, Republican Sen. Tom Tiffany. “I believe this is the most appropriate way for our chief justice to be named.” A proposed Senate bill, an amendment that would establish age limits for Supreme Court justices that would remove Chief Justice Abrahamson, 81, from the court altogether, would appear to belie that notion.

Either way, Abrahamson’s tenure as chief justice is likely over, as is the liberal minority’s primary means of asserting itself. The chief justice has no more power than the associates but can delay decisions she disagrees with using procedural tools. Abrahamson, and much of the strength to resist the tightening grip of special interests, seems to be fading away.