Well, now, this is interesting. Sen. Elizabeth Warren went to Kentucky to campaign for Allison Lundergan Grimes, the Democratic Secretary of State who’s looking to unseat Senate Minority Leader Mitch McConnell. The Louisville Courier-Journal reported that “a wide range of people from college students to people in their 80s attended the event at (the University of Louisville), billed as a college affordability rally.”

“I’m a little surprised to be here,” said Warren, “partly because I’m a little surprised to be in the United States Senate. I am the daughter of a janitor and I ended up in the United States Senate. America is truly a great place.”

Intentionally or not, Warren’s invitation sends a message. A Southern campaign asked a Massachusetts progressive (and a Harvard professor, no less!) to campaign for it in a close-fought race with one of the country’s leading conservatives.

Remember, we’re talking about Rand Paul country here. Some smart people have clearly concluded that progressive economic populism is a winning strategy in the South.Warren made several appearances in Kentucky. A veteran South Carolina politician found that unsurprising, saying of Warren: “She is against the corporate monoliths that the average blue-collar Southern [finds] anathema.”

The Grimes campaign knows what it’s doing. Despite having been dismissed as being too young and too liberal to pose a serious threat to the powerful and well-known incumbent, Grimes has pulled close to McConnell in most polling. (Some polls even show her in the lead.)

Grimes has assembled a talented and high-priced team of consultants, including top Democratic pollster Mark Mellman. We can be sure the decision to invite Warren wasn’t made lightly, but was the product of careful research and polling. The Grimes team clearly concluded that Warren’s brand of anti-Wall Street, pro-Main Street populism was a winning message.

They were undoubtedly helped to reach that conclusion by last month’s polling, funded by Americans for Tax Fairness, which showed that a large majority of Kentucky voters support Grimes’ position on closing corporate tax loopholes to fund a new bridge project. McConnell opposes closing the loopholes.

Grimes’ campaign has emphasized both generational and gender shifts, emphasizing the fact that she will represent millennials and women – and will defend these constituencies from the economic attacks McConnell has led in the Senate.

But identity politics alone won’t cut it if you’re peddling the same-old-same-old as an economic message. Warren’s messaging is clearly populist in both tone and substance. To these ends, Warren and Grimes emphasized Warren’s proposal to provide student debt relief at the “college affordability rally.”

And while she’s careful not to portray herself as a dissident in her own party, Warren’s pitch runs directly against the pro-corporate, Wall Street “centrist” line that has governed national Democratic politics since Bill Clinton’s ascendancy in 1992.

Warren’s recent editorial on “the Citigroup clique” highlighted the differences in her economic approach. She wrote about a single poorly-managed institution – one that has benefited greatly from Federal government actions – which has been linked to an outsized share of Democratic economic appointees. As Warren notes, “three of the last four Treasury secretaries under Democratic presidents have had Citigroup affiliations before or after their Treasury service.”

While Warren’s editorial concentrated on Obama appointments, observations like these are also a rebuke to the Wall Street-friendly Clinton administration.Positions like these put Warren’s brand of populism squarely at odds with her party’s corporate-friendly leadership. So do her uncompromising position on the need to end Wall Street’s exploitation of ordinary Americans and her call to expand, not cut, Social Security benefits.

What should Democrats in Washington take away from Warren’s visit to Kentucky? In addition to demonstrating that populism sells everywhere, it’s also a clear sign that the discredited “Third Way” agenda of corporate Democrats – an agenda that has dominated the national party for more than two decades – doesn’t sell.

After all, they’re not inviting Rep. Steny Hoyer to Louisville.And what does it tell Hillary Clinton, the Democrats’ presumptive nominee-by-acclamation for 2016? It demonstrates Bill’s old-fashioned triangulation – the means by which the Democratic Party moved itself toward the corporate right – has passed its sell-by date, even in Bill’s native South.

This move could also help Hillary and her advisers understand why there was so much blowback from her “we’re not rich” comments. As Robert Reich wrote recently, people were really questioning “whether all that income from big corporations and Wall Street put (the Clintons) on the side of the privileged and powerful, rather than on the side of ordinary Americans.”

When politicians amass great wealth from private corporations it makes people wonder about them– who their friends are, who influences their thinking, and who they’ll be looking out for should they regain power.

As Elizabeth Warren said recently, “people don’t have to wonder who side I’m on.” It’s incumbent upon any Democrat running for office, from Hillary Clinton on down, to make their own loyalties equally clear.

Which side are you on? That age-old line may sound divisive to today’s Washington ears, but it reflects today’s fundamental economic reality: policies which have consistently favored the few can no longer provide security or opportunity for the many.

Progressive populism isn’t a divisive political strategy. It’s a rational response to the world in 2014.

Which side are you on? That’s a question people will be asking all their politicians from now on, implicitly or explicitly. As Reich notes, a recent Pew poll found that “even 69 percent of young conservative-leaning voters agree the system favors the powerful.”

All across the country, across racial and class divides, and from left to right on the political spectrum, people want to know if their leaders support them in a struggle for an equitable economy. Americans understand that, in Warren’s words, “the game is rigged” – politically, economically, even in the halls of justice. They want to know if candidates are willing to help un-rig it.

This isn’t 1992, or even 1999. Times changed when Wall Street greed broke the back of the middle class and wounded the economy. Political reality changed when people realized that their wealth has been redirected upward for decades, that the promise of a good life and the opportunity for advancement had been eroded beyond sustainability for most Americans.

Alison Lundergan Grimes is reportedly close to the Clintons, and Bill is said to have helped her win the nomination. But her invitation to Elizabeth Warren strategy suggests that she and her advisors recognize this new political reality.

The national party should, too. Democrats who persist in their old triangulating ways will soon find themselves out of touch – economically, generationally, and geographically. Old ways, as the Neil Young song says, can be a ball and chain.

It’s unclear yet whether Grimes can pull off an upset victory. But she clearly has a shot, thanks to a feisty and populist-themed campaign. She is sending the country a message with her choices, including her choice of advocates.

Warren spent the weekend in Kentucky, but she already has new travel plans. She’s been invited to speak on behalf of another Democratic candidate – in West Virginia.

Which raises a question for the Clinton team and other Democrats in Washington: Are you paying attention?