Eric and Ivanka Trump in New York on May 1, 2014. (Brendan Mcdermid/Reuters)

THERE HAS been a fair amount of chortling over the fact that two of Donald Trump’s children won’t be able to vote for him in New York’s upcoming presidential primary. Their failure to register as Republicans may indeed, as his delighted critics were quick to point out, be another sign of Mr. Trump running a mistake-prone campaign. But their disenfranchisement is also indicative of the needless barriers that prevent far too many people from casting ballots. That is no laughing matter.

Ivanka and Eric Trump ran afoul of New York’s overly restrictive voting laws. New York does not allow same-day registration, party primaries are open only to registered Democrats and Republicans, and new voters must register at least 25 days in advance in order to participate. Most absurdly, anyone registered to vote who wanted to change their party registration to vote in Tuesday’s primary needed to have done so by Oct. 9 of last year. This is the rule that tripped up the unaffiliated Trumps. Six months before the primary? What purpose does that serve beyond suppressing democracy?

With the primaries in New York unusually competitive this year, the Trumps are not the only ones finding themselves shut out. Chances are a lot of those college students who jammed Wednesday’s rally for Sen. Bernie Sanders (I-Vt.) may be independent, first-time voters who will find out Tuesday they can’t vote. Susan Lerner, executive director of the state’s Common Cause affiliate, told the Atlantic: “We’re hearing from a lot of really well-engaged, well-informed people who were not aware that the deadline was last October 9. . . . There’s no justification for it.”

And while New York’s rules are among the nation’s most restrictive, the Empire State is far from alone in using an arcane system of voter registration. According to the Brennan Center for Justice at New York University School of Law, 1 in 4 eligible voters is not on voter rolls, and 1 in 8 registration records is invalid or has serious errors. What is needed are reforms — such as automatic registration using reliable information from government lists or online access so voters can check and update registration — to modernize the system and make it easier to vote.

Sadly, though, the trend seems to be moving in the opposite direction. Witness the proliferation of state laws requiring voters to present photo IDs at the polls or requiring proof of citizenship to register. Or the long lines in the recent Arizona primary that kept thousands of voters waiting for as long as five hours, a vivid illustration of not providing sufficient resources for voting.

Donald Trump's children say they're not registered to vote in New York's April 19 primary. How did that happen? (Peter Stevenson/The Washington Post)

Ivanka and Eric Trump are right to feel embarrassed about not voting Tuesday. But the true guilty parties are those responsible for maintaining high barriers to the franchise.