Democratic Senate candidate Elizabeth Warren, right, takes questions from members of the media as Massachusetts Gov. Deval Patrick, left, looks on during an event at Warren's campaigns headquarters Wednesday in Somerville, Mass. (Steven Senne/AP)

It started as a one-day story, a chuckle on conservative talk radio in Boston.

In late April, the Boston Herald reported that Democratic Senate candidate Elizabeth Warren had been identified as a Native American by her bosses at Harvard Law School. At the time, the school was trying to play up the diversity of its faculty.

Warren said her relatives told her that she has a fraction of American Indian heritage. She said she didn’t know that Harvard had identified her, officially, as an ethnic minority.

Late Wednesday, Warren acknowledged that it had been her, after all, who told Harvard and another university employer that she was Native American.

“At some point after I was hired by them, I . . . provided that information to the University of Pennsylvania and Harvard,” Warren’s statement said. “My Native American heritage is part of who I am, I’m proud of it, and I have been open about it.”

The explanation for the changing story: Warren’s campaign said she had forgotten events from the 1990s. But already, her epic fumble of a simple question threatened to change the dynamic of the Senate race in Massachusetts, one of the most-watched contests of this election year.

Warren had learned an iron law of politics: Bad denials make little things big.

The episode could have been a minor nuisance for the campaign. In a race in which the economy, jobs and debt are the overriding issues, it’s unlikely that whether Warren is Native American would matter all that much to voters.

But Warren has turned what could have been a small problem into a major story line by not coming out with everything she knew about the episode from the start.

At a news conference after a campaign event Thursday, her Republican opponent, Sen. Scott Brown, said that the controversy “goes to somebody’s character and it goes to their truthfulness and integrity, and it is up to the voters to decide how much that matters.”

“Everything I hear from people,” Brown said, “it matters a lot.”

Warren, a professor on leave from Harvard, helped President Obama create the Consumer Financial Protection Bureau after the 2008 financial crisis. She is now trying to unseat Brown, who won a surprise victory in a 2010 special election to replace the late Edward M. Kennedy (D).

Warren has become a liberal champion and sought to make her campaign about the “level playing field.” She said Brown and congressional Republicans were letting big companies and rich people avoid their fair share of taxes and regulation.

“Washington is rigged to work for those who can hire an army of lobbyists and an army of lawyers to get special deals,” Warren says on her Web site. “It isn’t working for small businesses and middle-class families. That has to change.”

Since the controversy, however, the race has been defined for her. It has been about whether Warren had tilted her own playing field — by playing up an ethnic identity she didn’t deserve. Warren has insisted that her heritage had nothing to do with her hiring.

“I am very proud of my Native American heritage, thank you,” Warren told the Herald on April 27, the day after the story first emerged. Warren said then that she could not recall listing herself that way when applying to schools or looking for jobs. Warren said she thought that Harvard might have learned of her heritage — family lore holds that she is part Cherokee and Delaware — through informal conversations with other faculty members.

“I listed myself in the directory in the hopes that it might mean that I would be invited to a luncheon . . . with people who are like I am,” Warren told the Herald on May 2. By then, it had been discovered that she had listed herself as a minority in a professional directory of law professors.

“There are real issues middle-class families are dealing with every day, and that’s where Elizabeth is focused,” Warren spokeswoman Alethea Harney told the Herald on May 27. By then, the Herald reported that Warren was declining to answer any questions about her ethnic identity.

Finally, after more digging from local reporters, Warren came clean Wednesday. On Thursday, in a last attempt to control the story, she sought to turn the outrage back on Brown. Earlier that day, Brown had made a crack about Warren relying on her parents’ stories: “My mom and dad have told me a lot of things, too, but it’s not accurate.”

“Scott Brown’s comments about my parents are totally out of line. I resent him questioning their honesty,” Warren said in a statement. She said Brown ought to apologize.

He didn’t.

“Especially in these type of things,” Brown had said earlier in the day, “when you’re checking a box and you’re getting benefits that are entitled to people who need them and who historically have been discriminated upon, and you have others relying on those representations, it is a problem.”