For more than a decade, special interests have engaged in increasingly partisan efforts to tilt the scales of justice, spending tens of millions of dollars to elect judges whom they believe fit their political beliefs. Now these assaults on America’s courts are expanding in troubling new ways and in dimensions we have never witnessed.

In states as dissimilar as Florida and Iowa, interest groups are seeking to oust judges because they disagree with a few rulings in controversial cases. By focusing on retention elections — a historically low-key vote focusing on judges’ professional qualifications — these groups have threatened to puncture a protective shield that keeps politics outside the courthouse.

In recent months, political party leaders have joined the assault in these states, breaking with local tradition and calling for removal of state supreme court justices. These party leaders, with their partisan declarations in a nonpartisan realm, threaten to utterly destroy the protective shield.

As lifetime jurists and former chief justices of the supreme courts of Arizona and Indiana, we believe citizens should be concerned. If judges cannot make hard calls based on the law, without looking over their shoulder for threats of retaliation, it will become harder for our justice system to fulfill its traditional responsibility to uphold the Constitution and protect Americans’ rights.

In retention elections, only the incumbent judge appears on the ballot, and voters choose “yes” or “no” to decide whether to grant the judge another term. This model, used at least some of the time for 20 state supreme courts, is based upon the principle that we should give voters a check on professional wrongdoing, while keeping politics and campaign spending to a minimum.

Unfortunately, that ideal is gravely at risk. When national political stars barnstorm Iowa to pillory a judge, and when political leaders in two presidential swing states publicly endorse the removal of qualified justices for partisan ends, they have crossed the line.

The threat is growing. Two years ago, five states saw retention-election challenges of a scope rarely seen before and in Iowa, three supreme court justices were denied retention over a single ruling. This year, political partisans have escalated the attacks by publicly joining the fight, with out-of-state funders at their side.

To ensure that strategies to politicize our courts don’t become the wave of the future, we must stand up to halt them now.

In Iowa, the state GOP is urging voters to deny retention to Justice David Wiggins, who joined the unanimous 2009 decision on marriage rights for same-sex couples. Iowa’s Republican Party chairman says it’s time to “help end the bullying of activist judges once and for all.” Former Senator Rick Santorum of Pennsylvania and Louisiana Governor Bobby Jindal appeared with the ouster campaign.

In Florida, three justices are up for retention. They have drawn the wrath of partisan leaders and special interests over rulings in a few controversial cases, one involving federal health care law. Now the state GOP finds them “too extreme not just for Florida, but for America too.”

Voters in Iowa and Florida adopted retention elections to give citizens a way to consider removing a judge in the rare instance he or she is unfit for office, whether for ethical lapses, for exhibiting general incompetence, or lacking the temperament to hear and decide cases fairly and impartially.

But the new tactics in retention elections undermine those goals. The tactics of the special-interest groups and partisan leaders are aimed at intimidating judges over decisions made on the bench. If they succeed, this country’s proud history of a fair and independent judiciary is placed at risk.

We were initially appointed by Republican governors to our respective supreme courts. Voters granted us retention multiple times. We have no political agenda in speaking out. Rather, we fear that our courts are under fire for doing their job — and that political attacks today threaten to interfere with judges fairly and impartially following the rule of law tomorrow.

Transforming judicial elections into referenda on a few rulings in controversial cases threatens this impartiality. It creates a profound risk that Americans seeking a fair day in court will instead get caught up in the nation’s political wars.

Ruth V. McGregor is a retired chief justice of the Arizona Supreme Court; Randall T. Shepard is a retired chief justice of the Indiana Supreme Court. They are members of the board of directors of Justice at Stake, a nonpartisan coalition to keep courts fair and impartial.