Elizabeth Warren has a Native American problem.

The Harvard Law professor challenging Massachusetts Republican Sen. Scott Brown is facing increasing scrutiny over use of Native American heritage in her legal career.

But it’s not Warren’s family tree that’s really at issue — it’s her ability to fight back. 

Let’s start with the facts as we know them.

On Friday, the Boston Herald reported that Harvard Law School had touted Warren as a Native American employee in the 1990s when the school was under fire for lack of diversity. Warren said she had no idea she was described as such until the Herald reported it, although she does have native ancestry. (A genealogist says Warren‘s great-great-great grandmother is listed as Cherokee.)

Elizabeth Warren faces her first real test. (Joshua Roberts/BLOOMBERG)

“The simple fact is that Elizabeth is proud of her heritage,’’ spokeswoman Alethea Harney said in a statement Sunday night, adding that it had nothing to do with her career advancement.

Officials involved in her hiring at Harvard, the University of Pennsylvania, the University of Texas and the University of Houston Law Center all told the New York Times that her ethnicity never came up in her hiring.

But the fact that this story has dribbled on for days shows how aggressive Brown has been, and raises questions about Warren’s ability to respond in kind.

“The Brown campaign has been more effective in the past few weeks and months being on offense and asking a lot of questions of Elizabeth Warren and the campaign, making a lot of accusations,” said Democratic strategist Mary Anne Marsh. “The Warren campaign should be doing the same — there’s plenty there.”

Brown himself told reporters Monday that “if there are questions, she should answer them” but said “I haven’t accused her of anything,” His campaign manager, Jim Barnett, was less coy, saying Warren needs to “apologize for participating in this hypocritical sham.”

Warren campaign manager Mindy Myers suggested the line of inquiry was sexist, comparing it to Brown’s argument that Supreme Court Justice Elena Kagan was not experienced enough for confirmation. But the campaign has largely laid low, instead trying to change the subject to the fact that Brown’s 23-year-old daughter is benefiting from the federal health-care law he opposed.

The most recent polling shows a dead heat in the race, with about a third of the crucial conservative and moderate Democrats still undecided. If Brown successfully defines Warren as untruthful and hypocritical while remaining well-liked himself, it could go a long way.