While most other Democrats are afraid to talk about the need for higher taxes and are running away from the problem, Elizabeth Warren, the leading Democratic candidate for a Senate seat in Massachusetts, has engaged the fight and is beginning to rally supporters.

Ms. Warren talks about the nation’s growing income inequality in a way that channels the force of the Occupy Wall Street movement but makes it palatable and understandable to a far wider swath of voters. She is provocative and assertive in her critique of corporate power and the well-paid lobbyists who protect it in Washington, and eloquent in her defense of an eroding middle class.

It is an informed and measured populism, and it helps explain why she immediately became the leading Democratic contender in the race to challenge Senator Scott Brown, the Republican who is up for re-election next year.