It's a fact that even in 2016, women are sorely underrepresented in politics. And their lack of parity comes into sharper focus when you consider this stat brought to light by recent election news: Three states have never sent a woman to Congress. Ever.

On Sept. 13, 2016, Delaware took a major step to scratch its name off that list. Lisa Blunt Rochester handily won her Democratic primary Tuesday night for the state's only congressional seat. The former labor secretary beat five men for the nomination.

Because Delaware is such a Democratic state, she's expected to easily win in November and become the first woman to represent Delaware in Congress. (She'd also be the state's first African American congressional representative.)

If all goes according to plan for Rochester, that would leave Mississippi and Vermont as the only two states who have never sent a woman to Congress, according to data from the Center for American Women and Politics at Rutgers University.

But it's not like these three states are an anomaly in American politics. In 2016, women make up half the U.S. population but just under 20 percent of Congress. Women are still vastly underrepresented in politics — as they have been for decades and will continue to be.

Consider: In 2007, Rep. Niki Tsongas (D) became the first woman to serve Massachusetts in Congress in a quarter-century. In 2012, Sen. Elizabeth Warren (D) became the first woman to represent the state in the U.S. Senate.

We're picking on Massachusetts here, but plenty of other states have made it into modern times without electing a woman to represent them in Congress. In Alaska, Sen. Lisa Murkowski (R) became the first woman elected to Congress from her state in 2004. (Her father actually appointed her in 2002.)

Idaho, which elected one woman to Congress in 1953 and another in 1995, hasn't elected a woman to Congress since 2001.

(The first state to elect a woman was Montana, which voted in Jeannette Rankin exactly a century ago — yes, four years before women officially won the right to vote.)

The problem isn't necessarily that voters don't think women make good lawmakers, say experts. It's that the path for women to become lawmakers isn't well paved — and there are some pretty big roadblocks in the way that men don't have to deal with.

"They win at the same rate as men," Debbie Walsh, director of the Center for American Women in Politics, told me in June. "We just aren't seeing enough of them."

Researchers and advocates for women in politics have a few theories on why women are so underrepresented in Congress and politics more generally:

  • There aren't enough women in state legislatures, which is one of the most direct pipelines for higher office.
  • Women have to contend with the sticky issue of whether voters like them in a way men don't. (Among the sometimes-head-spinning advice the nonpartisan Barbara Lee Family Foundation has given aspiring female politicians: Don't pose for a headshot. Do share personal anecdotes when explaining why you're passionate about an issue or how you've helped constituents. Don't take credit all the time for your accomplishments; every once in a while share credit with your team.)
  • There's a partisan gap. Women who run for public office are more likely to be Democrat than Republican. (Where are all the high-ranking GOP women? asked my colleague, Elise Viebeck, recently.)
  • Women of color are even less represented in politics, and they tend to represent only majority-minority districts.
  • Change in gender politics is moving very, very slowly. Between 2004 and 2014, the number of women in state legislatures increased by roughly 300 seats — an increase of less than 15 percent.

So, yes, Rochester's win Tuesday is one small step forward for womankind in politics. But experts tell me elections like hers are too few and far between to count as real change. Especially when it's 2016 and we're marking success by counting down the states that have yet to elect a woman to Congress.