Supreme Court Justice Ruth Bader Ginsburg has an "impossible dream": Before she leaves the Court, she would like to see Citizens United v. FEC – the 2010 Supreme Court decision that removed the cap on outside spending on elections – overturned.

"It won’t happen," Ginsburg told the New York Times when asked what she would like done while on the Court. "It would be an impossible dream. But I’d love to see Citizens United overruled."

It’s a hot-button issue. The ruling slackened restrictions on outside groups’ political expenditures, paving the way for Super PACs to accept unlimited contributions.

But unlike other controversial Supreme Court rulings – like Roe v. Wade on abortion or Obergefell v. Hodges on same-sex marriage – Citizens United has increasingly seen some bipartisan opposition. A 2015 Bloomberg national poll found 80 percent of Republicans and 83 percent of Democrats opposed the Citizens United ruling, signaling dissatisfaction with the role big money plays in politics.

Democratic presidential candidate Bernie Sanders made calls for campaign finance reform a central part of his campaign, and famously relied mainly on small donations for his fundraising. Donald Trump, too, touted his independence from big money because he mostly used his own funds for his primary bid. Hillary Clinton has also repeatedly said she wants the Citizens United decision reversed.

Not all politicians have been so critical, though. Marco Rubio defended big money in politics last year, and the vast majority of Republicans in Congress have tended to vote against various reform proposals from Democrats.

So Democrats have instead hoped change could happen in the courts. But as Ginsburg suggested, it’s always a tall order to overrule a Supreme Court decision. Georgetown University law professor David Cole explains why in the Atlantic:

The Court hesitates to overturn any past decision, but it is especially reluctant when a reversal means cutting back on a constitutional right, rather than establishing a new one (as pro-life opponents of Roe v. Wade have learned).

It might not be such an "impossible dream." Here’s how it could happen.

The Supreme Court has a 40-year precedent of ruling that monetary contributions are a form of political speech; in 1976, the Court ruled that the government cannot cap campaign spending, and in 2014 the Supreme Court ruled that a donor’s overall spending on federal campaigns cannot be capped. The notion that limiting money in politics limits free speech is also the leading conservative argument in favor of the Citizens United ruling.

Still, overruling Citizens United specifically might be more feasible if a liberal fills the seat of the late Justice Antonin Scalia. For instance, Clinton has claimed she would only nominate Supreme Court justices who are in favor of overruling Citizens United.

Vox’s Andrew Prokop argues that a change in the composition of the Supreme Court could have a big impact on campaign finance law, since "contentious campaign finance cases of the past decade have, very frequently, been decided by a bare five-vote majority of conservatives."

But Cole is more skeptical that really significant change will happen quickly. Instead of hoping for a Supreme Court silver bullet, he argues, campaign finance reformers need to wage a much broader and more gradual struggle on the state and local level and in academia — as gun rights activists and marriage equality reformers did.

And Cole writes that "promising campaign finance initiatives" in places like Maine, Connecticut, Arizona, Washington, and New York are a good place to start: