SINCE waving goodbye to the nation from a helicopter on January 20th, Barack Obama has mainly steered clear of the spotlight. Tomorrow, when America’s 44th president re-enters the fray with the first political appearance of his new civilian life, it won’t be to champion the Democratic take on health care, gun regulation or immigration policy. The fundraising event he is scheduled to attend has to do with gerrymandering, an issue few Americans get exercised about or even understand. But the aim of the private event in Washington, DC is central to the mission of the Democratic Party in the decade to come: taking control of state legislatures and governor’s mansions to stanch the huge redistricting advantage Republicans grabbed after the 2010 census.

Gerrymandering—the practice of setting electoral lines to optimise the chances of one party over another—is a decennial sin of every majority party. Holding the reins to extend its reign, the party in control seldom demurs. Legislators might “pack” political opponents into a few districts, rendering their votes meaningless in other areas of the state. Or they may “crack” districts apart, parcelling out a majority in one district into several others where they have no hope of electing their favoured leaders. Republicans scored a pile of victories in recent state elections, making them the latest and most thorough sinners. A recent study by the Brennan Centre at the New York University law school shows that Republicans have drawn lines that effectively reserve 16 or 17 congressional seats for their incumbents. With Democrats in need of 24 more seats to take over the House of Representatives in the 2018 election, that safe GOP bloc may prove insurmountable during Donald Trump’s first presidential term.

Mr Obama’s appearance this week is on behalf of the National Democratic Redistricting Committee (NDRC), an organisation headed by Eric Holder, the former president's first attorney-general. The NDRC intends to develop a "targeted, state-by-state strategy that ensures Democrats can produce fairer maps in the 2021 redistricting process”. Aside from gunning to win key elections, the main NDRC tactic is fighting court battles to nullify maps that strongly disadvantage Democratic candidates. The group is piggybacking on the work of the Campaign Legal Centre (CLC), a nonpartisan organisation that opposes gerrymandering by Republicans and Democrats alike. Attorneys from CLC are behind Gill v Whitford, a case coming to the Supreme Court in the autumn that challenges Wisconsin's electoral maps. In 2012, 51% of Wisconsin voters pulled the lever for Democrats in state legislative races, but Republicans wound up with 60 of the 99 seats in the state assembly. By 2016, the vote was still virtually tied, but the GOP won 64 seats. The plaintiffs in Gill say that “Republicans...wield legislative power unearned by their actual appeal to Wisconsin’s voters” and deprive voters of their rights to free speech and the equal protection of the laws.

The fight against gerrymandering will be an uphill battle. First, Democrats are years behind their opponents. REDMAP, the Republican redistricting programme, was launched in 2010 and has, thus far, met its goal of building a “Republican stronghold in the US House of Representatives for the next decade”. Reversing those gains will require much more than just a deeply unpopular Republican in the White House. Second, the Supreme Court will not necessarily affirm the lower court’s decision that extreme partisan gerrymandering violates the constitution. Three decades ago, the justices refused to snuff out a Republican-drawn gerrymander in Indiana, and in 2004, they could not agree on a standard for determining when redistricting offends the constitution. But there is hope for Democrats this time around—and not only because Mr Obama is lending his support to the cause. Gill presents the Supreme Court with a new social-scientific metric for pinpointing when a gerrymander crosses that line—a mathematical analysis that may win over Anthony Kennedy, the justice most likely to swing the ruling one way or another.

Correction (July 14th): An earlier version of this post mistakenly implied that the National Democratic Redistricting Committee is steering the litigation in Gill v Whitford, the legal challenge to gerrymandering in Wisconsin. The post has been amended.