The two new senators, along with other newly elected members of Congress, are in Washington, D.C., for orientation this week. The Senate is back in session, for the first time following last week's election, as of Tuesday.

McCaskill, who earlier this week tweeted that it was "gonna be fun walking on the floor of the Senate" after winning a tough race in Missouri, seemed to appreciate the coincidence of a women-only "power meeting" happening in the Senate bathroom. 

"Gonna need a bigger bathroom," she tweeted.

Sen. Amy KlobucharAmy Jean KlobucharOvernight Health Care: Trump eases rules on insurance outside ObamaCare | HHS office on religious rights gets 300 complaints in a month | GOP chair eyes opioid bill vote by Memorial Day Overnight Regulation: Trump to take steps to ban bump stocks | Trump eases rules on insurance sold outside of ObamaCare | FCC to officially rescind net neutrality Thursday | Obama EPA chief: Reg rollback won't stand Dems seek reversal of nursing home regulatory rollback MORE (D-Minn.) later experienced a similar "traffic jam" in the women's restroom.

The percentage of women in the Senate is now 20 percent, counting the women elected last Tuesday — an historic high.

Updated at 4:01 p.m.