(CNN) - The Supreme Court's future is poised to turn into a defining battle in the 2020 presidential election, as justices consider taking up cases that touch some of the nation's most sensitive political divides.
With President Donald Trump's two appointments locking in a 5-4 majority for conservatives on the court and the court's two oldest members being among its four liberals, fears about its makeup -- and potentially backlash over its decisions -- are likely to become flashpoints for Trump and Democratic candidates alike.
An early glimpse at what's ahead came Tuesday when the Supreme Court, by a 5-4 vote, allowed Trump's ban on transgender troops in the military to go forward for now.
Democratic presidential hopefuls are using the Supreme Court ruling on the transgender troops ban to attack Trump.
"Transgender military members have the courage to serve our country and deserve to do so. We have to fight back to reverse this," tweeted California Sen. Kamala Harris, who launched her 2020 campaign this week.
Massachusetts Sen. Elizabeth Warren, another 2020 contender who has launched an exploratory committee, tweeted that "Banning troops based on gender identity is unconstitutional & makes us less safe."
"I'll fight tooth & nail until trans Americans are free to be themselves & serve their country without discrimination," she added.
Also on Tuesday, the justices set the stage for another ruling on a divisive issue by announcing they would take up a major Second Amendment case, their first gun rights case in nearly a decade. That dispute, testing a New York City regulation, would be heard in the fall with a decision likely in spring of 2020.
The Trump administration also on Tuesday asked the Supreme Court to review its efforts to include a question about citizenship on the 2020 census. Democrats have fiercely criticized such a question, arguing that it would lead immigrants to refuse to participate in the once-a-decade count of the United States' population.
Several other incendiary petitions for review are pending at the high court. In the wake of the volatile confirmation hearings for Justice Brett Kavanaugh, the justices had slowed down their consideration of some issues and delayed expected orders on whether they would take up a case or deny the appeal outright. Among them are disputes over Indiana abortion regulations -- rejected by lower court judges -- that would target a woman's reason for ending a pregnancy and require the burial of fetal remains, and petitions testing whether Title VII of the 1964 Civil Rights Act prohibiting workplace sex discrimination covers claims based on sexual orientation or gender identity. The justices have postponed action on the merits of the Trump administration's effort to phase out the Obama-era protections for young undocumented immigrants.
If the justices decide to take up any of these cases, they would be heard in the session that begins next October with decisions expected by June of 2020 -- right in the middle of a heated presidential campaign.
Also potentially facing the justices as the 2020 presidential campaign intensifies would be any disputes arising from the ongoing investigation led by special counsel Robert Mueller of Russia's interference in the 2016 election. And while talk of a Trump impeachment is merely that, at this point, if the House of Representatives were to impeach the president, Chief Justice John Roberts would preside over the subsequent trial in the Senate. (That is the one responsibility of the chief justice of the Supreme Court that is spelled out in the Constitution.)
Potential for vacancies
Looming large in Democrats' minds is the possibility of more vacancies.
The court was at the forefront of the 2016 campaign because Senate Republicans refused to confirm former President Barack Obama's nominee after Justice Antonin Scalia's death.
Now, two of the four liberal members of the court are in their 80s, with Justice Ruth Bader Ginsburg battling health problems in recent weeks. With a Republican majority in the Senate, another vacancy could set up a contentious election year confirmation battle.
Roberts has tried to shield the Supreme Court, as an institution, from today's polarized politics. After Trump disparaged a US district court judge who had ruled against the administration in November, by calling him an "Obama judge," Roberts issued a rare rebuke: "We do not have Obama judges or Trump judges, Bush judges or Clinton judges. What we have is an extraordinary group of dedicated judges doing their level best to do equal right to those appearing before them."
But Roberts and his colleagues also face an imperative to clear up conflicting rulings in lower courts and, in some cases such as the military transgender policy, plainly feel compelled to reverse lower court orders, even though the justices' votes reveal ideological, if not political, fault lines.
The five conservative justices were all appointed by Republican presidents, the four liberals by Democratic presidents. Three justices are over 70: Ginsburg, who will turn 87 in 2020 and is now recuperating from surgery to remove cancerous growths; Breyer, who will be 82 in 2020; and conservative Clarence Thomas, who will be 72 in 2020.
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