Liberal Democratic Sen. Elizabeth Warren could be found Monday stumping in the unlikeliest of places — West Virginia. Senate candidate Natalie Tennant invited her to the campaign trail. (Jeff Simon/The Washington Post)

Populist Sen. Elizabeth Warren (D-Mass.) got a rock-star reception during a standing-room-only campaign rally here Monday, as hundreds of liberal activists cheered her broadsides against corporate interests and voiced hopes that her presence might shift the political winds in an increasingly Republican state.

The rally on behalf of Senate candidate Natalie Tennant was the latest in a string of recent Warren appearances in red and blue states alike, where Democratic base voters have embraced her fiery message as an envoy to working-class voters frustrated with both Wall Street and the Obama administration.

“Our job is to fight for the families of America,” Warren said, speaking to a packed ballroom at the Clarion Hotel in West Virginia’s eastern panhandle. “Stitch up the tax loopholes so that millionaires and billionaires pay at the same tax rate as the people in this room.”

Warren stumped in Kentucky late last month for Democrat Alison Lundergan Grimes, who, like Tennant, is running for the Senate in a state easily won by Republican Mitt Romney in the 2012 presidential election. Later this week, the freshman senator and former Harvard professor will be in Michigan supporting Democratic Senate candidate Gary Peters.

Warren also has visited Oregon, Ohio, Washington and Minnesota this year and has made dozens of e-mail solicitations on behalf of Democratic Senate colleagues — an unusually aggressive effort by a senator who has repeatedly denied interest in a presidential campaign. In Kentucky, Warren raised more than $200,000 for Grimes, who is running against Senate Minority Leader Mitch McConnell (R).

Here in West Virginia — an early stage for Democrats with national ambitions going back to John F. Kennedy in 1960 — Warren was greeted as a progressive hero, with several attendees pleading with her to run for president. Tennant’s campaign hopes that Warren’s populist message will help her close the gap against her well-funded GOP opponent, Rep. Shelley Moore Capito.

“We’re sinking, we’re barely treading water in West Virginia,” said Danette Jones, a local Democrat, as Warren was swarmed by admirers after her speech. “We’re looking for someone who’s going to stop the back-scratching, and she’s one of those people.”

On the other side of the state in Charleston, Capito campaigned with Rep. Paul Ryan (R-Wis.), a conservative favorite and former Republican vice-presidential nominee. Capito sharply criticized Tennant for appearing with Warren, who supports the president’s push to lower carbon emissions — a controversial position in a state where the coal industry is one of the economy’s central drivers.

“West Virginians told us today that they want their next senator to stand up for an all-of-the-above energy agenda that embraces coal,” Capito said. “They want someone who will fix the problems with Obamacare. They want someone who will stop strangling regulations from killing jobs and small businesses. That’s exactly what I’m prepared to do.”

The dueling events are a microcosm of this year’s broader national debate ahead of the November midterms, with Ryan and Warren seen as their respective parties’ leaders on issues important to middle-class voters. Ryan, the House Budget Committee chairman, has spent months making speeches on poverty, while Warren — a longtime financial consumer advocate and bankruptcy expert — has traveled the country giving populist speeches as part of a tour for her latest book, “A Fighting Chance .”

Tennant remains the underdog in the hotly contested Senate race, with most polls showing Capito — a well-known daughter of a former West Virginia governor — comfortably ahead. Capito also has a fundraising advantage, bringing in more than $1 million last quarter compared with $777,000 raised by Tennant in the same period, according to campaign advisers.

The victor will succeed retiring Democratic Sen. John D. Rockefeller IV and become the Mountain State’s first female U.S. senator .

The trepidation that some Democrats feel in standing with President Obama — along with former secretary of state Hillary Rodham Clinton’s absence on the midterm campaign trail — has provided an opening for Warren, who excites the base voters and small-dollar donors critical to any Democratic contender’s chances.

Warren’s visit was perhaps the biggest moment so far in an otherwise sleepy race. Tennant said her only other major surrogate has been Sen. Heidi Heitkamp (N.D.), a freshman and moderate Democrat who is little known outside her state. Scores of cameras lined the back of the ballroom, and dozens of reporters clumped around two cloth-covered tables near the podium.

Warren, 65, — who has repeatedly said she will not seek the White House in 2016 — focused her pitch on pocketbook issues such as student loans and Social Security while blasting banks and big businesses for tilting federal laws in their favor. Again and again, Warren thrust her fists in the air as union members and college-age volunteers in the crowd roared their approval.

“Citibank and Goldman Sachs and all those other guys on Wall Street, they’ve got plenty of folks in the U.S. Senate willing to work on their side,” Warren said. “We need some more people willing to work on the side of America’s families. Natalie’s that fighter.”

Warren sought to link Capito to the financial sector, calling her one of its top allies in Congress. “When [Wall Street] needs her, she’s been there,” Warren said. “She’s out there for Wall Street, she’s leading the charge.”

Warren also knocked Republicans for opposing an increase to the federal minimum wage — a stance Democrats believe will hurt Capito in a state with one of the nation’s lowest per capita incomes.

In her remarks, Tennant took care to distance herself from Warren and President Obama on energy issues and talked up her support for coal companies. She said in an interview that Obama would have a “lot of explaining to do” if he visited West Virginia because of new proposals by the Environmental Protection Agency to cut carbon dioxide emissions from coal plants.

But Tennant also repeatedly praised Warren as the rare national Democrat who could help win over undecided voters, many of whom have soured on Obama’s agenda but remain skeptical of the Republican Party’s commitment to the poor and blue-collar workers.

“When you look at Senator Warren, she’s just like West Virginians who have grown up in rural West Virginia,” Tennant said, citing Warren’s roots in Oklahoma and her years as a schoolteacher.

Tennant’s decision to invite Warren signals where she stands on the tension within the Democratic Party over whether to move more to the left as it tries to hold on to a slim Senate majority — and that she needs progressives to turn out in droves. Warren, who has frequently railed against the coziness of both parties with corporate titans and hedge-fund managers, is not beloved by some centrist Democratic financiers.

“Natalie Tennant and I do not agree on every issue,” Warren said, but added that they agree on the “core issue,” which she described as passing policies that lift the lives of working families.

“What is this election really about?” Warren asked the crowd, answering her own question: “It’s about whose side you stand on.”