The unknowns are unknown in part because there are few easy answers to some of the questions people want answered. Exactly what is a 21st-century economic plan that can do something about stagnant wages and the lack of economic mobility? Clinton and her Republican rivals face the same quandary on this. It is easy to identify the problems, but difficult from either the left or the right to present plausible alternatives to each party’s old policies.

Clinton’s history suggests no big-bang solution to these profound problems, but rather it shows a wealth of smaller initiatives that, however worthy or potentially effective, are not the stuff of grand or uplifting campaign rhetoric. That makes the challenge of answering the question about why she wants to be president all the more difficult. Almost no matter what she offers, people will want more — more specificity, more originality, more inspiration.

In that sense, there will be no new Hillary Clinton on the campaign trail beginning this coming week. She is a fully formed politician, with a lengthy résumé of accomplishments and considerable baggage from a lifetime of political battles. The question of whether there is a new Clinton may preoccupy much of the commentary about her latest candidacy, but it is something of a diversion. Anyone looking for definitive proof probably will be disappointed.