I agree that if Harris gets the nomination, Martin Heinrich is probably someone she will consider seriously. This article from
Business Insider had some insights into him:
Conversations and emails with ten New Mexico Democrats who have worked with the senator at various points in his political ascent produced a consensus view of the senator as a no-nonsense policymaker with ambiguous aspirations for higher office at best.
Heinrich's decision to avoid the spotlight has largely kept him off the long lists of Democrats itching to run against Trump in 2020.
"He has an excellent reputation here in New Mexico," Bernalillo County Democratic chairman Bill Peifer said. "However, I don't think that the junior senator from tiny (population-wise) New Mexico would do well on the national stage. I'm sure that if the 2020 nominee would ask him to run for vice president he'd agree, but that particular choice is usually dictated, in part, by who hails from a 'must win' state."
Several New Mexico Democrats acknowledged that although Heinrich was not the type of campaigner who feeds off energy in the rooms like former President Bill Clinton, his relationships with core Democratic constituencies in New Mexico has strengthened his campaign appearances.
"What happens in politics is your ambition evolves," [former Governor] Bill Richardson said. "He has the right stuff if he decides to run. He has the intellect, he has the boldness, he has the experience, he has the presence. The question is: Does he have the interest?"
https://www.businessinsider.com/why-martin-heinrich-isnt-running-for-president-2017-6