But if history has shown anything, it is that it is difficult to predict how so-called electoral reforms might play out. That is especially true if the unexpected happens.

In a year when Democrats are making an all-out assault on Republican-held congressional seats in California, Hunter was viewed as one of the longer-shot targets — unless he was indicted (it was known that he was under investigation). His opponent is Ammar Campa-Najjar, 28, who worked in Barack Obama’s White House and is making his first bid for major office.

In a more traditional political system, the Republican Party would step in, nudge Hunter out and replace him with a more palatable candidate. Officeholders have certainly been known to get indicted. But it appears no one planned for this eventuality in drafting the top-two system.

“There exists no process in California elections code for Duncan Hunter to remove his name from the November ballot (or replace him),” said Sam Mahood, a spokesman for the secretary of state.

So can voters write in someone else’s name on the ballot?

“There can be no write-in candidates for the November general election,” Mahood added.

These are the kinds of circumstances that test the skills of the nation’s best election lawyers, who no doubt will be poking around for loopholes in the days ahead.

The system was adopted over the objections of Democratic and Republican leaders, who warned that it could result in major-party candidates not making it through the crowded June runoffs, as almost happened this year. This latest development is likely to give them one more bit of ammunition in their argument to scrap the system.

This article originally appeared in The New York Times.

Adam Nagourney and Inyoung Kang © 2018 The New York Times