When Sen. Barbara Boxer (D) confirmed in January that she would not seek reelection in 2016, the announcement could have marked the end of an era -- an era of women.

Since the early 1990s, Boxer and Dianne Feinstein (D) have formed California's all-woman Senate delegation, speaking for one of the nation’s most populous and diverse states on a national stage. With Boxer and Feinstein in office for more than two decades, the idea of women guiding national policy and political discourse became what political scientists often call "normalized." For a generation of California residents, there was nothing remarkable and certainly not unusual about women in positions of political authority.

And the contest to replace Boxer -- along with some other key Senate races nationwide -- has become a kind of affirmation of that idea.

Five months after Boxer’s announcement, two women -- both women of color -- have announced that they are running for her seat. California Attorney General Kamala Harris, who is black and Indian American, and 10-term Rep. Loretta Sanchez, a Latina, have officially declared their candidacies, with Harris as the strong favorite and Sanchez as her top foe. (Five Republican men also are running, but the GOP isn't expected to compete in solidly blue California.)

Women in power might amount to political normcore in California, but women -- and certainly women of color -- remain relatively scarce in the federal office. Right now, just 104 serve in the House and the Senate. Of these, 33 are women of color. And, if Harris or Sanchez make it through California’s new primary system and prevail in the general election, one of them will become only the third woman of color to serve in the U.S. Senate.

"I joke with my classes that I study this stuff for a living," said Kelly Ditmar, a political scientist at Rutgers University-New Brunswick and a scholar at the school's Center for American Women and Politics. "And when somebody says 'U.S. senator' to me,  I still have an old white guy in my mind. But there's no question that some of our norms about women and power are beginning to shift."

The story is somewhat similar in New Hampshire, where Jeanne Shaheen, a Democrat, has been a part of that state’s Senate delegation since 2009, and was joined two years later by Kelly Ayotte (R). Right now, Shaheen and Ayotte form another all-female Senate delegation. And after the coming election, that distinction is likely to remain in place. Many of the state’s politicos anticipate that New Hampshire Gov. Margaret “Maggie” Hassan, a Democrat, will challenge Ayotte. Hassan has not yet declared her candidacy. If she does, Hassan and Ayotte probably would form another all women front-runner contingent, this time in a state in which both of the major parties can mount a real competition for voters.

Going back through history, such match-ups between women in top-tier races are rare -- but becoming less so. Boxer faced another woman, former Hewlett-Packard chief executive Carly Fiorina, in her 2010 reelection race. In 2012, now-Sen. Mazie Hirono beat former Hawaii governor Linda Lingle (R). And in 2014, now-Sen. Shelley Moore Capito (R) beat West Virginia Secretary of State Natalie Tennant (D).

Nationwide, other women -- including women of color -- are seeking Senate seats and are well-positioned but facing male competition.

In Nevada, former attorney general Catherine Cortez Masto, a Democrat, is vying to replace Sen. Harry Reid in a race that is still taking shape. If she wins, Masto would be the first Hispanic woman to serve in the U.S. Senate and the first woman to represent Nevada in that body.

In Maryland, another state with a relatively recent history of women in federal office in the person of Sen. Barbara Mikulski, Rep. Donna Edwards is running against another Democrat, Rep. Chris Van Hollen. No Republicans have officially entered that race, and the GOP isn't likely to be competitive.

In Arizona, Rep. Ann Kirkpatrick (D) just jumped in the race against longtime Sen. John McCain, the 2008 Republican presidential nominee, who also faces a primary challenge from a woman, state Sen. Kelli Ward.

In Illinois, the state that sent to Washington one of the two women of color who have served in the Senate (Carol Moseley Braun), Rep. Tammy Duckworth, who is part Thai, is the front-runner to face Sen. Mark Kirk (R). Other hopefuls include Chicago Urban League President Andrea Zopp and possibly Rep. Robin Kelly. Kirk’s reelection bid has been described as one of the toughest in the country.

And in North Carolina, we're still waiting to hear whether recently unseated former senator Kay Hagan (D) will challenge Sen. Richard Burr (R).

In all of these cases, the ranks of women in Congress could grow. But that progress has often been slow.