(CNN) There is no old boys club that is older or clubbier than the United States Senate.

If you've ever covered it or even sat in the visitor's gallery during a vote, you know what I am talking about. For years, the Senate seemed like an institution frozen in time: A group of largely old, largely white men backslapping and yukking it up -- all thrilled to be part of this most exclusive club in the world.

Sure, that has changed somewhat over the years. There are now 21 total female senators -- 16 Democrats and 5 Republicans. Washington Sen. Patty Murray of Washington is a member of the Democratic leadership.

But, for the most part, the Senate remains more "Mad Men" than "Girls."

That's what makes Wednesday's decision by a group of female Democratic Senators to come out en masse to call for the resignation of Minnesota Sen. Al Franken , a fellow Democrat, so important. They were reacting to a growing number of accusations from women that he had groped them or tried to kiss them without their consent.

"Our history, our culture is changing so dramatically in this country, so fast," Murray told CNN's Lauren Fox . "It's time for elected officials at all levels to stand up and take responsibility for who we are and what we stand for."

It began with a statement issued on Facebook by New York Sen. Kirsten Gillibrand just after noon. She wrote, in part:

"While Senator Franken is entitled to have the Ethics Committee conclude its review, I believe it would be better for our country if he sent a clear message that any kind of mistreatment of women in our society isn't acceptable by stepping aside to let someone else serve."

Those coordinated calls for a Franken resignation set off an avalanche within the Democratic Party. Soon, more than a dozen of Franken's colleagues were calling on him to step aside immediately. And within an hour, Franken's office announced that he would make a statement tomorrow in Minnesota -- a statement virtually certain to be his resignation.

It was a stunning show of force by the Democratic women in the Senate. And while it came as a surprise to most people, the idea of moving in force against Franken had been percolating for some time now, one congressional aide familiar with the ongoing discussions among the female senators told CNN's Sunlen Serfaty . The source added to Serfaty that the group concluded that the allegations against Franken had reached a tipping point today. (On Wednesday, Politico reported about a new Franken accuser .)

Yes, there were politics involved here too.

Gillibrand, who was the first female Democratic senator to speak out, is regularly mentioned as a potential 2020 candidate against President Donald Trump. Ditto Harris. Same with Massachusetts Sen. Elizabeth Warren, who reportedly called Franken personally to tell him to quit . Sen. Amy Klobuchar, another 2020 possibility, held off on calling for Franken's resignation. But her reticence to do so is likely born of the fact that she and Franken are home-state colleagues.

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Given the ongoing cultural awakening to the massive problem of men behaving inappropriately toward women and the fact that more than a dozen women during the 2016 campaign alleged that Trump had sexually harassed them, being seen as a champion for women and a leading voice of the #metoo movement is a very powerful place to be.

Then there is the fact that in six days' time, Alabama voters may well elect Roy Moore as their next senator despite the fact that the Republican nominee faces a series of allegations that he pursued relationships with teenage girls when he was in his 30s -- and, in two cases, they say he assaulted them.

The contradiction of Democrats holding their tongues on Franken -- particularly as the allegations mounted -- while condemning Republicans for failing to push Moore out of the Alabama race gave the GOP a foothold in the moral high ground argument.

"Let me tell you the hypocrisy we see at every turn," White House senior counselor Kellyanne Conway told CNN's Chris Cuomo on "New Day" Wednesday. "Al Franken is in the Senate right now. He has admitted this."

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But simply because there is political gain to be had from calling on Franken to resign doesn't eclipse what a handful of female Democratic senators accomplished in the space of an hour today.

They decided enough was enough. That no matter what Franken said about the allegations, there were too many women coming forward to accuse him of inappropriate behavior. That silence was no longer good enough.

This marks a seminal moment in the history of the Senate. Today is the day that female Democratic senators asserted their power in ways that we have seen women across other parts of society -- like Hollywood and media -- do in the last few months.

This is a big deal.