Why Donald Trump's Kids Won't Be Voting for Him in New York's Primary

Two of Donald Trump's adult children — Ivanka and Eric — have spent months on the campaign trail trying to convince people to vote for their father in the Republican presidential primary. But when it comes time for New York's primary election next Tuesday, neither of them will be able to do the same.

New York has a closed primary system, which means that only voters registered as Democrats or Republicans can vote in their respective party's primary. Both Ivanka and Eric missed the deadline to change their registration from unaffiliated to Republican and therefore will have to sit out next week's election. Trump's eldest son, Donald Jr., is a registered Republican in New York, so at least one of Trump's children will be able to vote for their father.

Trump addressed the matter during an appearance on Fox and Friends Monday. "They had a long time to register and they were, you know, unaware of the rules," Trump said. "They feel very, very guilty."

The deadline to change your party registration in New York is October 9, 2015 — the earliest in the country and fully six months before the actual primary (first-time voters had until March 25 to register). New York's especially strict elections rules mean that voters were forced to commit themselves to a party at a time when the race looked very different than it does today. This year's deadline came after only two Republican debates and before the Democrats had even debated at all. Back then, Ben Carson was Trump's closest contender for first place in a very crowded GOP field. And Marco Rubio and Jeb Bush topped political prognosticators' lists for the Republican nomination. Times have changed.

Ivanka and Eric aren't the only New Yorkers who missed the early deadline. Nearly 3 million people, or 27 percent of all active voters in New York, were not registered with either major party ahead of the deadline, according to the state elections board. None of them will be able to vote on April 19.

This matters in a presidential election dominated by "outsider" candidates like this one. A closed primary hurts anti-establishment candidates like Trump and Bernie Sanders the most, both of whom have performed better in open primaries where people can vote for any candidate regardless of their party affiliation. Much of Trump and Sanders' support has come from independent voters who have not previously been affiliated with a mainstream party. But in New York, those independents will not be permitted to vote in either the Democratic or Republican primaries on Election Day, even if they are registered voters.

What's more, many of those voters likely won't discover they can't cast a primary ballot until they get turned away at the polls on Election Day. Voters can still register with a party after the October 9 deadline, but there is no law mandating that the state informs them that their party registration won't count for the 2016 presidential primary, according to Think Progress.

Some Sanders supporters saw this issue coming and set up an entire website dedicated to informing voters about New York's election laws. But Trump's campaign, who only set up their New York operation last week, was not quite as prepared. Eric and Ivanka discovered this the hard way.

Follow Olivia Becker on Twitter: @oliviaLbecker