Women will occupy a record number of Senate seats — roughly one in five — in January, following historic victories in Tuesday’s balloting.

As many as six women could win election to the Senate once all ballots are counted, with victors already declared in Wisconsin, Massachusetts, Hawaii and Nebraska, and races too close to call in North Dakota and Nevada. Currently, 17 women — the most yet — serve in the chamber, and two of them, Republicans Olympia Snowe of Maine and Kay Bailey Hutchison of Texas, are retiring.

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Elizabeth Warren and husband Bruce Mann The Associated Press

All but one of the women who prevailed at the ballot box are Democrats. They probably benefited from the momentum of President Obama’s campaign and from Senate Democrats’ painting Republicans as waging a “war against women” that would limit reproductive rights, said Barbara Lee, founder and president of the Barbara Lee Family Foundation, which seeks to boost women’s representation in elective office.

“The more women hold office, the more the barriers dissipate,” Lee said in an interview.

Before midnight, it was clear that the Senate would retain a record number of women, and it would be a bipartisan effort.

First, Nebraska state Sen. Deb Fischer, R, was declared the winner over former two-term U.S. Sen. Bob Kerrey, D, for an open seat. Minutes later, Harvard professor Elizabeth Warren, whose attacks on Wall Street fueled her political rise in the Democratic Party, won her race against Massachusetts incumbent Sen. Scott Brown, R.

The record was set less than an hour later, when U.S. Rep. Tammy Baldwin, D-Wis., claimed victory over Tommy Thompson, R, the state’s longest-serving governor and secretary of Health and Human Services under President George W. Bush. Like Warren, Baldwin is the first woman to represent her state in the Senate.

Women have been making steady gains since the election of 1992, dubbed the Year of the Woman, when seven women were in the U.S. Senate. Gains have been slower in state legislatures, which provide a pipeline to higher office, Female representation stands at 24 percent, just three percentage points higher than two decades ago, according to the Center for American Women and Politics at Rutgers University in New Brunswick, N.J.

For statewide elective office, one of the clearest paths to governorships, it has risen 1 percentage point in that time, to 23 percent, down from a high of 28 percent in 2001.

This election year’s wins include the seat being vacated by retiring Sen. Daniel Akaka, D-Hawaii. There, U.S. Rep. Mazie Hirono, D, defeated former Gov. Linda Lingle, R.

In North Dakota, former state Attorney General Heidi Heitkamp was leading Rep. Rick Berg, R, by almost 51 percent to 49 percent, with 99 percent of the state’s precincts reporting. Both are seeking to replace Sen. Kent Conrad, D, chairman of the Senate Budget Committee.

Likewise, a race in Nevada hasn’t been called. There, Rep. Shelley Berkley, D, is facing off against incumbent Sen. Dean Heller, R.

In New Mexico, former Rep. Heather Wilson, R, lost her battle for the seat of retiring Sen. Jeff Bingaman, D, to Rep. Martin Heinrich, D.

All Democratic incumbent female senators up for re-election this year were returned to the chamber. They include Claire McCaskill of Missouri, Debbie Stabenow of Michigan, Dianne Feinstein of California and Amy Klobuchar of Minnesota.

While four states today are represented by two female senators — New Hampshire, Maine, California and Washington — that’s one area that will see a decline in the next congressional session. Snowe, who has represented Maine in the chamber for three terms, will be replaced by independent Angus King, a former Maine governor.

In neighboring New Hampshire, female incumbent Sens. Kelly Ayotte, R, and Jeanne Shaheen, D, will be part of another first. New Hampshire in January becomes the only state to have women in the governor’s mansion, in both Senate seats, and in all House seats.

That comes after Maggie Hassan, D, won her race for governor and Democrats Carol Shea-Porter and Ann Kuster wrested New Hampshire’s two House seats from the incumbent Republicans, both men.