Progressive commentator Sam Seder said Monday that progressive heavyweights Sens. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) and Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) shouldn't try to appeal to centrist Democrats.

"I think just trying to appeal to the center," Seder, host of liberal talk radio program The Majority Report, told Hill.TV in response to a question over what would be the biggest mistake either candidate could make.

“Both of them have a message to the extent that people perceive it as authentic,” he continued, adding their messages are “what’s going to bring out their voters.”

Seder also emphasized that there isn’t a clear sense of who the Democratic electorate is going to be, particularly in early state primaries.

“It’s sort of hard to know who is really going to show up in these early state primaries,” he said.

Both Warren and Sanders have emerged as top challengers to front-runner Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE in recent months.

A new poll found Warren leading former the former vice president for the first time in Iowa.

According to a Des Moines Register/CNN/Mediacom survey, 22 percent of likely Democratic caucusgoers in Iowa back Warren for president. Another 20 percent named Biden, the current front-runner, as their top choice.

—Tess Bonn