Following a legal review, the matchup is set in what may be New Jersey's most unconventional race for mayor this fall.

The wife of President Trump's key re-election campaign advisor is running against a losing Congressional candidate who, on the same day, won the local Democratic primary for mayor without actually entering it.

The municipal clerk in Mendham Borough certified Friday the nomination of Mark Washburne. He finished a distant third in the 11th District Congressional primary on Tuesday, only to later discover that he received 74 write-in votes for mayor in his hometown, enough to propel him to victory.

Washburne will face Mendham Councilwoman Christine Serrano Glassner, who defeated Councilman Stanley Witczak to win the Republican primary.

Her husband is Michael Glassner, Trump's deputy campaign manager for the 2016 election.

In February, Glassner was named chief operating officer of Trump's 2020 re-election bid, 13 months after he was chosen as executive director.

During his unsuccessful campaign for Congress, Washburne said that, if elected, he would vote to impeach Trump.

Election Day is Nov. 6.

Republicans have a big edge over Democrats in Mendham Borough, which is home to about 5,000. Ex-Gov. Chris Christie lives in neighboring Mendham Township.

When no Democrats filed to run for mayor, it appeared that the winner of the Republican primary would face no opposition in the fall.

Then, in mid-May, the chair of the Mendham Democrats approached Washburne and asked if he would be willing to accept a write-in nomination.

Washburne, in disclosing the offer Thursday, said he had agreed despite holding out hope he would someone overtake Mikie Sherrill, who ended up getting 77 percent of the vote in a 5-candidate Congressional race.

Washburne received 74 write-in votes for mayor, well beyond the 16 required -- but his candidacy for mayor still needed to clear a legal review.

Mendham municipal attorney Fred Semrau advised allowing Washburne to proceed, despite not finding any other examples of a candidate in a federal election simultaneously winning a local election as a write-in.

"As unusual as it may have seemed, there wasn't anything that specifically would have precluded his nomination," Semrau said.

The winner will succeed Mayor Neil Henry, a Republican in office since 2006 who decided not to seek a fourth term.

Serrano Glassner was a New Jersey delegate to the 2016 Republican convention. Her council term runs through 2019.

"I'll work hard to earn the support of all Mendham voters and eventually the privilege to serve our great community as their citizen-mayor," she said.

Washburne is a history professor at County College of Morris and perhaps better known for his daily running streak dating to 1989. He is president of the U.S Running Streak Association, an organization whose members commit to running at least a mile per day.

His race for Congress was his first run for office.

Asked about switching so quickly to running for mayor, Washburne said, "Democrats haven't won in a really long time, so it's an honor to give people a choice."

Rob Jennings may be reached at rjennings@njadvancemedia.com. Follow him on Twitter @RobJenningsNJ. Find NJ.com on Facebook.