One of the more overlooked outcomes of the 2018 Democratic primary was the defeat of four incumbent state lawmakers. All were men.

Three of the four victorious challengers were women.

On top of that was the strange case of Smyrna-based House District 40, being vacated by Republican Rich Golick. Erick Allen had run for the seat three times before, but was beaten in last May's Democratic primary by Sandra Bullock — who was not the actress, had never run for office before and not campaigned.

Bullock quickly withdrew, and Allen — though he lost the primary — now has a desk in the Legislature.

State Sen. Steve Henson of Tucker very nearly joined that casualty list. The leader of Senate Democrats for the last eight years finished only 111 votes ahead of an unknown primary challenger, Sabrina McKenzie. It was his first contested primary in 16 years.

We are in the midst of a revolution at the state Capitol, one in which the absence of a Y chromosome carries (at long last, some would argue) a distinct political advantage.

A few days ago, Henson, 60, announced that he would not seek another term in 2020. The senator said he felt confident that he could still hold his seat next year, but only at the expense of two higher priorities — his off-campus business and his job as a recruiter for the next class of Democratic senators.

“Getting out and working hard, I strengthened myself in the last election,” Henson said. “But I did know that to retain office, I would have to go out and work very hard to make sure I stayed in contact with my constituents, because a lot of people who have not been involved in the district are getting out and participating.”

All of which means that Henson now holds a unique spot in the state Senate.

Only a few years ago, if you were to launch a discussion about “the only white male Democrat” exiting a given political body, most would interpret the phrase as an invitation to talk about race.

Now the emphasis is on gender.

By no means are we alone. In recent days, Washington has been hypnotized by Speaker Nancy Pelosi’s confrontation with four freshmen members of the U.S. House — all women of color.

On Tuesday, a North Carolina effort by GOP elites to back a woman for Congress — part of a strategy to stop the hemorrhaging of female voters — failed miserably. Dr. Joan Perry, a pediatrician, lost by 20 points to Greg Murphy, a Republican state lawmaker, in the contest to replace the late U.S. Rep. Walter Jones.

In Georgia, the Senate minority leader’s decision to depart is a sign that, for Democrats, success won’t come without growing pains.

On the Senate floor, Henson is a quiet strategist, an affable and slightly rumpled figure. He had made no fresh ideological shift that might explain last year’s close call. He remains an unapologetic progressive with strong union ties.

Neither has Senate District 41, which straddles DeKalb and Gwinnett counties, experienced a sudden change in demographics. It remains roughly 50 percent African-American – just as when its boundaries were last drawn in 2012, Henson said.

What has changed is the rise of Donald Trump, who drove an entirely new crop of voters to the polls last year. “On the Gwinnett side of the district, we saw a lot of people vote who have never voted before — almost triple the [usual] number,” Henson said. Many were angered by a president who has spoken of women as playthings. To those newcomers, Henson was a stranger. And male.

Actually, Henson was first elected to the Senate in 1990. Sonny Perdue, the future Republican governor, was in that class. A group photo of the 56-member class hangs on Henson’s wall.

That year, the Senate had only two women members, both of whom became bookends in that photo. Democrat Cathey Steinberg of DeKalb County was on one side. Republican Sallie Newbill of Sandy Springs was on the other. (It would be another two years before Nadine Thomas, a DeKalb Democrat, became the first African-American woman elected to the body.)

Henson left the Senate in 1998 to make an unsuccessful run for state labor commissioner. He returned in 2002, just in time to see four Democrats change parties and place the chamber under GOP control.

Despite spending the latter half of his political career in the minority, next year Henson will leave a 21-member caucus that is on the upswing – and distinctly female. Thirteen Democratic senators are women. By comparison, the 34-member Republican caucus includes only two women.

Democratic numbers are likely to increase next year. The three potential candidates currently kicking the tires on the race to replace Henson — the suburban district leans Democratic — are female.

Two Senate districts in metro Atlanta, held by Republicans John Albers of Roswell and P.K. Martin of Lawrenceville, were won last year by Democrat Stacey Abrams.

Both incumbents will be targeted — likely by women, who are becoming the Democratic go-to demographic for the foreseeable future. Georgia’s new anti-abortion law isn’t the only motivator, Henson said.

“I think more women are likely to run when they see that Republicans are so out of touch that they don’t realize that [House Bill] 481 has true health care implications for women and their safety and well-being,” he said. “But there are so many other issues, I don’t think it will be the sole reason anybody runs.”

An expanding female majority in the Senate Democratic caucus also means that Henson’s successor, who would take over in January 2021, will likely be a woman, said Gloria Butler of Stone Mountain, who currently serves as caucus chairman.

That’s important. On the other side of the Capitol, in the House, a similar leadership position proved to be an effective launching pad for Stacey Abrams’ gubernatorial bid.

But Butler said the impact of the gender shift is already underway on the Senate side. Three of the newer members of the caucus, Elena Parent and Jen Jordan of Atlanta, and Zahra Karinshak of Duluth, are attorneys whose presence this year sharpened debates over abortion and Senate rules dealing with sexual harassment, Butler said.

“It’s wonderful that we have that talent — that we can depend on,” she said. And male members of the caucus are learning to defer.

“We have more women speaking out,” Butler said. “And the men are kind of standing back a little bit and letting that happen. I’m not sure that we want them to get out of the conversation. I don’t think we want that. But they let us carry the conversation — conversations that were always carried by men.”