Democratic strategist Andrew Feldman warned Monday that Sen. 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.) needs to be prepared for attacks on all fronts in the fourth Democratic presidential debate this week in Ohio.

“Elizabeth Warren needs to have her armor on, because I think that people are going to come after her,” Feldman, founder of progressive firm Feldman Strategies, told Hill.TV.

“Everyone’s going to be coming at Elizabeth Warren,” he added.

Feldman’s comments come a day after Sanders, in a rare move, highlighted a key difference between him and Warren’s economic philosophies.

Sanders told Jonathan Karl of ABC News that Warren is “capitalist through her bones,” and asserted that he is the only presidential contender who will challenge corporate greed in Washington.

"I am, I believe, the only candidate who's going to say to the ruling class of this country, 'Enough. Enough with your greed, and with your corruption. We need real change in this country,'" Sanders said over the weekend.

Both Sanders and Warren have steered clear of direct attacks on each other, but Warren has been gaining momentum in recent months as both candidates look to win over the progressive portion of the party's base.

The RealClearPolitics polling index shows Warren in second place with 26 percent support among Democratic voters, followed by Sanders with 15 percent support.

Some statewide polls show Warren running neck-and-neck with former Vice President 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, the Democratic primary front-runner.

According to a new CBS poll, Biden and Warren are each tied at 22 percent among Iowa voters for the top spot.

The same CBS survey showed that Warren leads Biden by 8 percentage points, with 32 percent support, in New Hampshire, another early voting state.

The top 12 candidates are slated to take the debate stage on Tuesday night in Ohio.

—Tess Bonn