Chief Justice John Roberts Jr. began the Supreme Court’s term last fall seeking to assure the American public that his court does not ‘‘serve one party or one interest.’’

He will end it playing a pivotal role in two of the most politically consequential decisions the court has made in years.

One initiative is to include a citizenship question in the 2020 Census, which has fueled a partisan showdown on Capitol Hill. The other could outlaw the partisan gerrymandering techniques that were essential to Republican dominance at the state and congressional level over the past decade.

The politically weighted decisions, by a court in which the five conservatives were chosen by Republican presidents and the four liberals were nominated by Democrats, threaten to undermine Roberts’s efforts to portray the court as independent.


They are among two dozen cases the court must decide in the next two weeks, and never before has the spotlight focused so intently on the 64-year-old chief justice.

Roberts sits physically at the middle of the bench in the grand courtroom and now, for the first time since he joined the court in 2005, at the center of the court’s ideological spectrum. With the retirement of Justice Anthony Kennedy last summer, the most important justice on the Roberts Court became Roberts himself.

Roberts in the past has shown himself to be far more conservative than Kennedy, and Justice Ruth Bader Ginsburg suggested recently that has not changed.

Kennedy’s retirement, she told a group of judges and lawyers in New York, was ‘‘the event of greatest consequence for the current term, and perhaps for many terms ahead.’’

Roberts has been on a mission to convince the public that if the court is ideologically split, it is about law, not politics.

‘‘We do not sit on opposite sides of an aisle, we do not caucus in separate rooms, we do not serve one party or one interest, we serve one nation,’’ Roberts told an audience at the University of Minnesota in October.


He repeated the message at Belmont University in Nashville in February. ‘‘People need to know we’re not doing politics,’’ he said.

In between was the well-publicized spat with President Trump, who just before Thanksgiving criticized an ‘‘Obama judge’’ serving on a lower court who had ruled against his administration in a contentious case centered on immigration policy and border security.

But Brianne J. Gorod, chief counsel of the liberal Constitutional Accountability Center, said the many questions about whether Trump’s citizenship question is intended to benefit Republicans should be a warning for Roberts.

‘‘If Roberts votes to uphold this plainly unlawful administration action, it will give credence to Trump’s claim that he can simply look to the conservative justices on the Supreme Court to save him,’’ Gorod wrote on the Take Care blog.

‘‘That would be a deeply troubling state of affairs — both for the court and for the country.’’

Lawyers challenging the census question filed an unusual motion Wednesday, asking the court to either affirm lower courts that have ruled the question can’t be added to the census form, or delay a ruling until those courts can examine new evidence about a Republican political operative’s role in Commerce Secretary Wilbur Ross’s decision to add the citizenship question, which critics contend is discriminatory, politically motivated, and will result in an undercount of the nation’s immigrant population.


‘‘This court should not bless the secretary’s decision on this tainted record, under a shadow that the truth will later come to light,’’ they said.

In the gerrymandering cases, the court’s decision could have far-reaching results for how elections are conducted in the United States. The court often polices redistricting plans drawn by the states to ensure they do not discriminate based on race, but it has never found a plan so infected by politics that it violates voters’ rights.

On the surface, a decision that courts have no role in trying to decide when there has been too much partisan interference would not help Republicans more than Democrats. The court is considering a North Carolina plan drawn by Republicans to give the party a huge edge, and a Maryland congressional district drawn by Democrats to oust a longtime Republican incumbent.

But as a practical matter, being able to draw districts to help the party in control currently benefits the GOP. The party is in control of both the governorship and legislature in 22 states, compared to 14 for Democrats.