Sen. Elizabeth Warren and Sen. Bernie Sanders haven’t been acting like rivals for the Democratic presidential nomination.

“I’m with Bernie on Medicare For All,” Warren announced at the first debate in June.

“Elizabeth is absolutely right,” Sanders said at the second debate last month when Warren discussed trade and protectionism.

Far from elbowing each other out of the far-left lane of the Democratic primary, Warren and Sanders have jointly sought to fend off attacks from the more moderate candidates. The two progressives advocate for transformational change over incremental improvements to boost low- and middle-income Americans, backing policies of a massive scale such as Medicare For All and the Green New Deal.

Political experts say that, at this point of the primary, Warren of Massachusetts and Sanders of Vermont benefit more from working with than against each other.

It’s about strategy as much as principle, said Monica Klein, a New York-based Democratic consultant.

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“One, it doesn’t bode well for either of them to attack the other because one of them will need the other’s voters,” said Klein, co-founder of Seneca Strategies. “And two, they both want a progressive, populist president, so it makes more sense for them to support that vision.”

Warren and Sanders have ideological allies among the vocal, media-savvy freshman House members who became stars after defeating long-serving moderate Democrats in the 2018 midterms — a cadre that includes Rep. Alexandria Ocasio-Cortez of the Bronx.

Democratic front-runner and former Vice President Joe Biden and other pragmatists have assailed the policies, saying they’re unrealistic and they threaten to alienate swing voters in an election where Democrats of all shades of blue agree the end goal is unseating Republican President Donald Trump.

Progressive groups say the Warren-Sanders partnership has inspired a necessary shift leftward.

“More is more,” said Adam Green, co-founder of the Progressive Change Campaign Committee, adding of the most recent debate: “They were a powerful force to be reckoned with together, which had the net impact of making both of their ideas be perceived by voters as more mainstream, which is good when a top criteria is electability against Trump.”

Among the five highest-polling candidates in the primary, Warren and Sanders are on the left end of the spectrum. Both seek to scrap private health insurance in favor of a government-run system. Critics of Medicare For All argue that many Americans who have private insurance want to keep it and are more concerned about cost than coverage.

Closer to the center is Biden, who opposes Medicare For All — the government-run system — and wants to build on Obamacare by adding a public option.

In between are Sen. Kamala Harris of California, who supports Medicare For All with private providers as part of the equation, and Mayor Pete Buttigieg of Indiana, who calls his plan “Medicare for all who want it.”

It remains to be seen how long the Warren-Sanders cease-fire will hold.

Warren, a former Harvard Law School professor, is ascendant in the polls as Sanders, a self-described Democratic socialist who also served in the House, has been falling. A national Quinnipiac University poll earlier this month showed her at 21 percent among Democrats, up 6 points from last month, versus Sanders at 14 percent, down 3 points.

“In some future time — if they’re the last two candidates in the race or the last two out of three — then there’s probably room for a friendly discussion about the best way to implement a bold, progressive, transformational presidency,” said Green of the PCCC, which backs Warren.

After all, their bases don’t completely overlap.

The Quinnipiac poll showed Warren had more support among higher-earning voters — those making more than $50,000 — than Sanders did, 44 percent to 17 percent. It also showed her leading him by a 20-point margin among voters identifying as “very liberal.”

Quinnipiac polling analyst Mary Snow noted another category in which Warren has led over the months and one that her campaign has capitalizing on by using the slogan, "Warren has a plan for that."

“She has shown strength consistently in the question of who has the best policy ideas,” Snow said.

Thirty-two percent of Democrats in this month's Quinnipiac poll say Warren has the best policy ideas compared with 17 percent for Biden and16 percent for Sanders.