Some politicians know they want to be in public office and scramble to come up with the reason why. Sen. Elizabeth Warren is an accidental, improbable politician – a self-described “outsider” – who knows exactly what she wants to accomplish on the inside.

The Massachusetts Democrat insists that she’s not running for president, and there’s little reason to doubt her – although, interestingly, Warren sticks doggedly to the present tense to describe her intentions.

I asked Warren about this phrasing the other afternoon over iced tea mixed with lemonade at a restaurant near her Capitol Hill office. In these precincts, senator sightings are commonplace but, even here, Warren enjoys celebrity status; the manager promptly presented Warren with a copy of her memoir, “A Fighting Chance,” to sign.

Why not simply declare that she will not run for president in 2016? “I am not running for president in 2016,” Warren responded. Yes, I pressed, but why not say, “I am not running and I will not run”?

“Because we can’t get so deeply involved in the politics of 2016 that we miss the importance of the issues in front of us today in July of 2014 and the 2014 election,” Warren replied, jumping slightly ahead of the calendar. “It is absolutely crucial to stay focused right now on this set of issues and that’s what I’m doing.”

Hmmm. “The point is not to try to create any ambiguity,” Warren added. “I am not running. I think I am being definitive.”

But to read Warren’s book, and to hear the passion in her voice as she talks about the plight of the middle class and the Washington deck stacked so decidedly against them, is to wonder, as she might say in her folksy Oklahoma way: Why the heck not?

Political consultants constantly hunt for the personal narrative to marry with campaign message. Agree with her politics or not, for Warren, autobiography is ideology: She has lived the one-mishap-away-from-bankruptcy existence that she is determined to help provide a governmental cushion against.

“My daddy was a maintenance man and my mother worked the phones at Sears,” Warren writes in the opening pages. She describes how, after the family station wagon was repossessed and her father, hospitalized with heart trouble, was out of work, her mother squeezed into her best black dress to apply for a minimum-wage job.

Warren’s self-described mission is to ensure that the next generation enjoys the same “fighting chance” she had; her current crusade is to lower interest rates on existing student loans, paid for by closing corporate tax loopholes.

In that, Warren is characteristically relentless. In her book, she recounts pressing President Obama so hard about whether he will name her to head the new Consumer Financial Protection Bureau that he complains, “You’re jamming me, Elizabeth.” She lectures then-Treasury Secretary Timothy Geithner – “I think I may have raised my voice a little” – for failing to buckle his seat belt.

It is no coincidence, as my colleague Dan Balz has observed, that Warren chose the title “A Fighting Chance” while Hillary Clinton opted for “Hard Choices.” For Warren, the fight is clear – the little guy against predatory banks and big corporate interests – and the choices not all that hard.

Warren joined other Democratic women senators in a letter urging Clinton to run. But unlike some colleagues, “bless their hearts,” Warren has not endorsed the former secretary of state, arguing that since Clinton has not announced there is no endorsement to be made.

Do you think, I asked, that Clinton has the fire that you want to see in a presidential candidate, to fight for the middle class? “I think she has fought for important issues for a very long time, and if she decides to run I think it will be for those reasons,” Warren responded, not entirely on point.

Is that a yes? “It is a statement of fact,” Warren replied. “It’s what she’s done.”

When I ask about what she made of Clinton’s book-tour comment about being “dead broke” on leaving the White House, Warren paused for a full 19 seconds.

“Um, I was surprised,” she finally said. “But, families across this country are working so hard to hold together,” she added, veering into an unrelated disquisition about young people falling behind their parents and the false promise of trickle-down economics.

As to “Hard Choices,” Warren said, “I have the book. I just got it and I’m looking forward to reading it. I will be on an airplane tomorrow and I will start.”

Ruth Marcus is a columnist for The Washington Post. She can be contacted at:

ruthmarcus@washpost.com