What, exactly, does President Trump have to hide in his tax returns?

That question is one of many that hangs over the Trump presidency — and it’s one of the reasons that this presidency sometimes feels so strangely vulnerable, as if it could implode at any moment.

Did he work the system to pay pathetically low income taxes? Are there business connections that would raise even more difficult questions about potential conflicts?

We don’t know, and we might never find out. The leak and subsequent release of two pages of Trump’s 2005 taxes last week told us nothing meaningful. The timing of such a selective revelation that just happened to be favorable to Trump is more than a little suspicious, suggesting the cherry-picked documents might have been leaked by Trump himself.

Regardless, New Jersey’s Democratic leaders are trying to do what they can to prevent a repeat of Trump’s tax-return suppression. Last week the Legislature approved a bill that would compel presidential and vice presidential candidates to release their federal tax returns for the previous five years. Other states are considering a similar move.

Grandstanding by the Democrats? Sure. It’s not even clear whether the state has the authority to force release of the returns. But it’s worth the attempt. This should be a nonpartisan issue applying as it does only to future races that would equally affect both sides. Yet the legislative vote broke along party lines, with Republicans balking. Why? Protecting Trump’s potential re-election bid? Or do they imagine that Republicans in general would have more to hide?

Assembly Minority Leader Jon Bramnick even suggested New Jersey similarly mandate the tax returns for gubernatorial and legislative races. We’d support that as well, although Bramnick understood Democrats wouldn’t bite. But why the snarky response? Democrats running for president are wealthy too. They’re just as likely to have secrets to protect. The Dems were certainly motivated by Trump’s actions, but it’s the president who put a bullseye on his own back. Of course Gov. Chris Christie will almost certainly veto the measure.

Trump’s refusal to release the returns is for the moment an anomaly, standing as it does in contrast to 40 years of precedent in presidential races. But it could easily mark the beginning of a new trend. Future candidates can simply cite the Trump example. Trump has insisted he cannot release the records because he’s being audited. It’s a weak excuse at best — but expect it to last awhile.

Democrats are trying to score political points, which is why Republicans are resistant. But those tax returns matter. Without them, trust erodes. Trump’s odd bromance with Russian President Vladimir Putin is uncomfortable enough without wondering if Trump is trying to keep the lid on his own business relationships with Russia. What other conflicts could compromise future actions by the White House?

Americans will suffer if future presidential candidates, shown the way to secrecy by Donald Trump, decide we don’t have a right or a reason to see their tax returns.