But Warren's ability to move easily from blue states to red states is proof she has "become a serious player" on the national stage, said longtime Democratic consultant Bob Shrum.
"One thing that has become clear is that the caricature of her as somehow or other too far left is entirely wrong," he said. "She's campaigning in West Virginia, she's campaigning in Kentucky … the [campaign] people there are smart enough to know what's going to help them and what's going to hurt them."
Warren's star power was certainly on display in West Virginia on Monday, when she walked on stage to a standing ovation and deafening applause from the audience of more than 400 people, some of whom shouted things like "2016!" or "2020!" Much of her speech focused on the need to fight back against Wall Street and on the student-loan interest-rate legislation she's championed, both issues that played well with the crowd.
That's similar to the explanation Warren's team gave for why she's hitting the trail so frequently: She wants to elect more Democrats to the Senate to support the Democratic agenda. The candidates she's helping are thrilled to have her boosting them—and, should they get elected, could be her allies on critical issues going forward.
"Senator Warren believes we need more people in Washington speaking up for American families who just want a fair shot to succeed, and she will continue to support 2014 candidates so that Democrats maintain control of the Senate," said spokeswoman Lacey Rose.
National Democrats say Warren's populist rhetoric taps into the anger among working-class voters of all political persuasions, who are angry with Wall Street and angry with Washington. That message works particularly well in West Virginia, where Tennant's campaign is trying hard to portray GOP candidate Shelley Moore Capito as too cozy with Wall Street.
For Warren, testing her message in less-friendly territory will help broaden her appeal as she aims to demonstrate—both to her party and to voters across the country—that she's a political force to be reckoned with.
"Elizabeth Warren can prove that a progressive, populist message is very powerful and successful in a red state," said Charles Chamberlain, executive director of the progressive group Democracy for America.
Warren gave a nod to the differences she has with Tennant, saying on Monday that they're in agreement where it matters.
"So here's the deal: Natalie Tennant and I do not agree on every issue," Warren told the crowd. "But on the core issues … Natalie and I agree. I watch Natalie, I see her. She's strong, she's independent, she doesn't let anybody roll over her. What I like about Natalie is, she's ready to fight … for America's families."
Besides the specific message Warren brings to the table, she's also filling a void in Democratic politics this year: The party has a shortage of viable campaign-trail surrogates.