WASHINGTON — In a rare break from the usual tradition of House incumbents either backing each other or staying neutral in a primary, Illinois Democratic Reps. Jan Schakowsky and Luis Gutierrez on Wednesday endorsed challenger Marie Newman over Rep. Dan Lipinski.

“It’s not easy to endorse a challenger over a colleague in the House of Representatives,” Gutierrez said at a press conference on Capitol Hill with Newman and Schakowsky.

“Especially when that colleague is a member of your party. But I think this is a very special and at the same time a very dangerous time,” he said.

Said Schakowsky, “this is not personal,” with the split, she said, “based on issues.”

Lipinski told me when we talked after the press conference that working-class issues — not gay rights and abortion — are what the Democratic voters in his district care the most about.

The March 20 Illinois primary is one of the earliest in the nation and this intra-Democratic fight for the third congressional district seat will be a real time test of voter mood in this Trump era.

BRIEF OVERVIEW OF THOSE ISSUES: The main issues Schakowsky and Gutierrez cite for the public split are abortion and gay rights and immigration — all signature issues for them.

“People largely know where I am on all of these issues,” Lipinski said.

Lipinski is a longtime abortion foe.

He told me on Wednesday he has changed his views on immigration through the years. Gutierrez, who has made immigration reform a crusade, will be testing that contention.

Lipinski’s history on immigration will be become a front-burner matter as the primary progresses.

As for gay rights: Lipinski said he accepts gay marriage as the settled law of the land. He stands out as a Democrat who has not co-sponsored the Equality Act — to amend the Civil Rights Act of 1964 to “include sex, sexual orientation, and gender identity among the prohibited categories of discrimination or segregation in places of public accommodation.”

He told me that’s because he is concerned about its impact on religious institutions.

BACKGROUND: This is the biggest primary challenge Lipinski, from Western Springs, has faced since 2008.

Lipinski had no primary rivals in 2016 and 2014; and nominal opponents in 2012 and 2010.

In 2008, Lipinski emerged from a four-man primary field with 53.8 percent of the vote.

There is no major GOP contender running. The victor in the March primary will represent the third district in Congress.

WHY THIS PRESSER WAS IN D.C. AND NOT CHICAGO: This contest is getting national attention because it’s about more than local politics.

A Democrat seen as right of center — Lipinski — is running in a primary against a progressive — Newman — at a time the Democratic party is looking to regain its footing in the wake of the election of President Donald Trump. That’s an evolving national theme.

Adding to the test tube factor: Bernie Sanders beat Hillary Clinton in this district in the 2016 Illinois primary. Will Newman, from La Grange, get the benefit of a new crop of newly motivated Democratic voters?

Newman is hoping that shining a national spotlight on these big endorsements will help in fundraising.

A reason for the endorsement, said Schakowsky, is “I am hoping that it will encourage some donors to decide that they would support Marie.”

DISTRICT DATA: The third congressional district is mainly Southwest Suburban turf with a slim corridor connecting it to Southwest Side wards in Chicago — especially 13, 14 and 23 — what’s left of the old Chicago machine.

According to an analysis from the Lipinski team, in the 2016 primary, 44 percent of the votes came from those old machine wards in Chicago, while about 9 percent came from the Will County suburbs, and about 47 from the Cook County suburbs.

Illinois House Speaker Michael Madigan, the chairman of the Democratic Party of Illinois — and the boss of the 13th Ward — has always protected Lipinski, the son of his ally, former Rep. William Lipinski, D-Ill.