WASHINGTON — Elizabeth Warren's team doesn't want to talk about Hillary Clinton, but that doesn't mean the 2020 presidential candidate isn't talking with her party's 2016 nominee.

The two women have kept a line of communication open since the Massachusetts senator decided to run for president — though only a conversation around the time of Warren's launch has been previously reported — according to several people familiar with their discussions who spoke to NBC on the condition of anonymity because of the political sensitivity of private interactions.

It’s hard to know exactly how many times they’ve reached out to each other — or precisely what they’ve discussed — in part because neither camp wants to reveal much of anything about their interaction and in part because they have each other's phone numbers, and there are many ways for two high-powered politicians to communicate that don’t involve their staffs.

One source was aware of just one additional call between Warren and Clinton since then. But a person who is close to Clinton said the contact has been substantial enough to merit attention, describing a conversation between the two as seemingly recent because it was "front of mind" for her.

"That has clearly not gone unnoticed, and I think she really appreciates that," the person close to Clinton said.

Clinton is a fraught subject for the Democratic contenders — perhaps for none so much as Warren, who, in the shadow of Clinton's defeat, is seeking to become the second woman to win the party's nod and the first woman elected president.

As she seeks to blend her movement-based progressive campaign with a Democratic establishment long wary of her populist brand of politics, Warren has been maintaining and creating relationships with a wide array of Democratic establishment figures. And if the race for nomination goes long — as many Democrats now predict — Clinton could become pivotal as an ally, an adversary or a neutral observer.

More immediately, Warren would no doubt like to win over support from Clinton voters, particularly women — and women of color — as she battles Sen. Bernie Sanders of Vermont, former Vice President Joe Biden and the rest of a field that trails the top-tier triumvirate.

But Warren has made little effort to publicly highlight ties to Clinton, who is perceived by many on the left as too centrist and who was defeated in an election Clinton and her allies believe was heavily colored by President Donald Trump waging a misogynistic campaign. To the extent that Democratic primary voters fear a repeat scenario in 2020 — and to the extent that she's competing with Sanders for the votes of progressives — there may be good reason for Warren to keep her distance from Clinton publicly.

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At the same time, people who know and like both women say there are more similarities between them than some of their partisans would like to admit. Each is a policy powerhouse with an uncommon command of details, and possess the ability to master new material quickly with a deep intellectual curiosity. Like Clinton, Warren focused the early part of her campaign on developing a raft of policy proposals and rolling them out.

More important, an explicit or implicit blessing from Clinton could help Warren if she finds herself battling for delegates and superdelegates at a contested Democratic convention next summer.

"Hillary Clinton would absolutely have influence over a number of delegates to this convention," said Deb Kozikowski, the vice chair of the Massachusetts Democratic Party.

Warren aides declined to discuss the relationship between the two women, the dates or content of their conversations, or the campaign's strategic thinking about whether to show proximity to, or distance from, Clinton. Clinton's spokesman did not return a call or a text message from NBC before publication.

Though Warren harshly criticized Clinton's vote for a 2001 overhaul of bankruptcy laws, the two have developed a healthy respect for each other in recent years. When Clinton was developing policies for her own campaign in 2015, her aides kept in close contact with Warren to give her an opportunity to raise concerns before they were rolled out.

By that point, Warren already had opted out of mounting her own campaign — disappointing many progressives — when she signed a letter, along with other Democratic women in the Senate encouraging Clinton to run. Later, as Clinton reviewed her options for a vice presidential running mate, Warren made a late ascent onto the short list on the strength of the excitement Clinton and her advisers thought Warren might bring to the ticket.

Warren told Bloomberg Businessweek this summer that she would have accepted the offer, but it went to Sen. Tim Kaine, D-Va.

Clinton has been impressed with Warren's campaign so far, according to a Democratic strategist who has spoken with her.

"She has applauded her about being serious and disciplined and loves that she is sticking to her guns," the strategist said, speaking on the condition of anonymity because Clinton's remarks were intended to remain private.

Clinton has relationships with most if not all of the Democratic candidates, and she met with or spoke to many of them at the start of this campaign cycle. Mayor Pete Buttigieg of South Bend, Indiana, sat down with Clinton in New York several months ago when his star was rising and he needed to clear the air following a report on his criticism of Clinton's campaign. But the contact with Warren appears to have been more than a courtesy call or a trip to the principal's office.

With a progressive base behind her, Warren's political need is to make establishment Democrats comfortable with her candidacy. Clinton, whose politics arguably have been closer to Biden's over the course of her career, has deep credibility in those circles.

But Clinton and Biden developed a rivalry when they worked in the Obama administration and as they both prepared for a 2016 campaign that Biden ultimately didn't enter. She also might take into consideration factors other than proximity on policy if she decides to back a candidate at some point.

Kozikowski, who has not endorsed a presidential candidate, said it would make sense for Clinton to be helpful to one of the women running if she can put her over the top.

"It would be counterproductive for the first woman nominee of the party to not be supportive of a woman who may go over that threshold," Kozikowski said.