Reliably Democratic Tempe may have a real race for the state Senate on its hands.

It's just unclear exactly why.

The trio of Democratic legislators now representing much of Tempe and part of Mesa have split up, with Rep. Isela Blanc forgoing reelection to the state House of Representatives to challenge Sen. Juan Mendez in the primary.

Mendez made it official last week that he is accepting the challenge.

He filed for reelection to the Senate alongside incumbent Rep. Athena Salman and newcomer Melody Hernandez, a first-responder who has been active in the local Democratic Party and will seek the House seat Blanc is vacating for her Senate bid.

A millennial slate of public officials

The three — Mendez, Salman and Hernandez — announced they would form a millennial slate with the goal of making their district the first represented at the Arizona Capitol entirely by members of their politically underrepresented generation.

"We are the generation inheriting an earth in crisis with public schools shattered by a disastrous conservative agenda, and we are done waiting for others to fix it," Mendez said in announcing the move.

Mendez is the oldest of the group at 34.

And perhaps the statement was a shot at Blanc, who is 47.

Blanc is quick to point to her experience as a formerly undocumented immigrant and as a mother who has lived in the area for more than 30 years.

Why are Blanc and Mendez facing off?

The primary, it seems, may come down to a choice not between policies but between personalities and experiences.

Blanc said they are not far apart on the issues, agreeing with Mendez 99.9% of the time, as she describes it.

Both are self-described progressives.

"I'm sure we are similar. (The race) goes beyond policy," said Blanc. "... It's the experience that I bring as a mom, as a community member."

Mendez and Blanc have different explanations of how they ended up facing each other in a primary for state Senate.

Blanc said they had an agreement that one of the legislators currently representing the district in the House would run for the Senate seat.

Mendez said they agreed he would serve until his term limit, along with Blanc.

Blanc's announcement in March that she would run for Senate was a surprise to both Mendez and Salman, he said.

The decision, which Mendez called unilateral, should be a red flag for voters, he said.

"Speaks volumes about the way she makes decisions," Mendez argued.

So far, they are the only choices in the district's Democratic primary for state Senate.

And Blanc describes that as a big reason for her campaign.

"It's really all about giving voters options," she said.

Patrick Morales and Debbie Nez-Manuel are running in the Democratic primary for the district's state House seats against Hernandez and Salman, making it a four-way race for nomination to the two seats. Morales is also a millennial.

Millennials want to represent a young district

If there is a district in the Valley where youth might be a particular plus, it could be this one.

It stretches across Tempe to parts of Mesa and the Salt River Indian Community. And as home to Arizona State University, the median age of resident in the district is about 28, lower than the state's median age of about 37.

Millennials — generally, people born between 1981 and 1996 — have been under-represented in the state Legislature when considering their proportion of the state's population, while Baby Boomers have been over-represented, according to data compiled by the National Conference of State Legislators.

Contact Andrew Oxford at andrew.oxford@arizonarepublic.com or on Twitter @andrewboxford.