Watching Hillary Clinton beaming sidewise onstage as Elizabeth Warren taunted Donald Trump brought the Wrigley twin ditty to mind: Double your pleasure, double your fun, with double good, double good, Doublemint gum.

Instead of two happy twins riding a tandem bicycle to celebrate chewing gum, the Clinton-Warren sixties sister-clones — wearing blond bobs and shades of blue — rode Trump with a gobsmacking double punch.

Railed the senator from Massachusetts: “Now, Donald Trump says he’ll make America great again. . . . It’s stamped on the front of his goofy hat. You want to see goofy? Look at him in that hat.”

This was her way of topping Trump’s repeated use of “goofy” to insult her.

And: “When Donald Trump says ‘great,’ I ask: ‘Great for who, exactly?’ ” she said. “When Donald Trump says he’ll make America great, he means make it even greater for rich guys just like Donald Trump. . . . That’s who Donald Trump is. . . . And watch out, because he will crush you into the dirt.”

Presumptive Democratic presidential nominee Hillary Clinton, right, with Sen. Elizabeth Warren (D-Mass.) at a rally in Cincinnati on June 27. (Melina Mara/The Washington Post)

And so the Twitter wars between a non-candidate and the presumptive Republican presidential nominee will likely continue. Doesn’t Trump realize that he’s the one running for president?

Clinton’s rally, the first to feature Warren, was followed by a sisterhood hug that only women can exchange. That simple embrace signified a new benchmark in women’s and American history and changed the political narrative for all time. Not only can a woman win a major party’s nomination, but also it’s possible that two women can team up as running mates.

The idea that Warren might become Clinton’s vice presidential pick has been floating around for a while and is appealing if only for the prospect that two women could fill an entire presidential ticket.

Warren certainly is as qualified as many men who have filled the role. She obviously doesn’t mind serving as the attack dog for Clinton. And Warren may be the one grinding Trump into the dirt, invective for invective. In a word, she’s fearless to his careless.

Warren and Clinton haven’t always been so cozy, but, for the eternal record, women differ from one another in as many ways as men do. Warren is further to the left than Clinton ever meant to be. And she comes far more naturally to a populist message. While Clinton was being forced leftward by Sen. Bernie Sanders (I-Vt.), Warren was continuing her years-long progressive crusade.

Her endorsement of Clinton and her new role as a rowdy, crowd-warming act constitute a bridge between Sanders supporters and the presumptive nominee they never wanted. Warren captures the anger and anti-1-percent angst of the liberal left and lays it like a wreath at the feet of the woman who would become the first female president.

Warren is a peace offering who aims to wage war on Trump. And she’s on to his greatest weakness. He can’t take a ribbing and he can’t stand being challenged by a woman. It gets under his skin like nothing else. Thus, when Warren says he looks goofy in a hat, he calls her Pocahontas (for her having said she has Native American blood).

What’s clear is that Warren won’t back down no matter what Trump tosses her way.

Speaking strictly as an observer, I think Trump may be losing his ranking as top draw in the political circus. If Warren stays on the stage, it’s nearly assured that all eyes will be on her — which might cause Clintonites some concern.

Like Trump, Warren has that certain something that fills arenas and draws people to their feet. That’s where the similarities end. A Harvard law professor before she ran for the U.S. Senate, Warren is smart, eloquent on consumer protection issues and passionately committed to well-defined principles. One needn’t agree with her to appreciate her vigor, as well as a steely-eyed softness that comes across in person.

Unlike Trump, she’s in possession of an agreeable personality. Even when yelling across a surging crowd, she manages to avoid sounding strident. Close up, she’s warm, engaging and nonthreatening.

Most important, she allows Clinton to step back from the fray and gives everyone a chance to imagine what a two-woman ticket could look like. Too much the same? Too soon for two? For whom?

It may be true, as someone wrote me, that Clinton’s greatest virtue is her opponent. But it’s also plain that Warren is her greatest asset.

Talk about a twofer.

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