The day before Elizabeth Warren announced she was leaving Harvard to run for the US Senate, she gave Deval Patrick a call to ask for advice, eager to hear what a novice campaigner could learn from a veteran.

“Always speak from the heart,’’ she recently recounted hearing from him back then. “People always know the difference.’’

Oh, and one other thing, he told her: “Stay hydrated.’’

She laughed. And ever since, she has made sure her car is well stocked with bottled water.

Now, as the former Massachusetts governor and the Bay State’s senior senator both seem to be positioning themselves for 2020 presidential runs — perhaps against each other — they could soon both need plenty of water as they shout themselves hoarse at campaign stop after stop, trying to stand apart from the pack — and each other.

On the issues, they are almost twins. But in the matter of style, their contrasting approaches offer a window into the debate coursing through the Democratic Party as a whole: how best to take on the strangely formidable force that is Donald Trump.

An eye for an eye? Or eyes on the prize? The party could turn to a challenger who makes no effort to conceal disdain for Trump, and counterpunches his every outrage. Or it could look for someone who offers a more positive message that can unite a fractured electorate.

Warren, whose most recent book is called “A Fighting Chance,’’ relishes her image as a fighter, always ready to battle with Trump and talk, even in the midst of a debate over financial regulations, of leaving “plenty of blood and teeth left on the floor.’’ Patrick’s memoir was called “A Reason to Believe,’’ and he built much of his career as a hopeful politician attempting to bring together disparate viewpoints.

“This is a microcosm of the larger debate of what’s going to happen in the party,’’ said David Axelrod, the former senior strategist for Barack Obama who has also advised Patrick.

“There is that body of thought that to beat Trump you’ve got to be as pugilistic as Trump,’’ he added. “There’s another body of thought that an exhausted nation is going to be looking for someone who can restore some sense of values and civility and lift up these institutions that have been torn apart. And I don’t know where that is going to end up.’’

There are other potential Massachusetts candidates — from US Representative Seth Moulton, who has already been to Iowa, where the first caucus vote is held, to John Kerry, who still muses about a presidential bid. But Patrick and Warren at this point seem to be the ones most actively considering entering what is expected to be a crowded field. They’ve both met with Obama, and they have taken meetings with potential donors in Manhattan.

“I love her as a person and as a senator,’’ Patrick told the Globe. “I think she brings a ton to the Commonwealth and to the party. And whatever she does, or I do, she will be my friend.’’

Warren was similarly effusive.

“Deval has a good heart and good ideas,’’ she said. “During his time as governor, his optimistic vision set a course for Massachusetts that has benefited millions of people in the Commonwealth. Bruce and I enjoy getting together with Deval and Diane, when we have time to talk at length about our families, our dogs, and our country. I’m honored to call Deval my friend.’’

Sources close to each potential candidate say they will make their own decision to run, without regard to the choice by the other. They see themselves as each having a distinct and different pathway to the nomination, so they would not feel politically encumbered if their home-state ally also decided to run.

“Elizabeth Warren will be very much a ‘Let’s take the fight to the streets,’ forward-looking, this is what the Democratic Party needs to be. We’re not progressive enough, female enough, fighter enough,’ ’’ said Scott Ferson, a longtime Massachusetts-based Democratic consultant. “Deval Patrick will be very much a cool reflection of the recent glory days. ‘Don’t we miss the civility and the inclusiveness that Barack Obama brought to the country? Don’t you want to be there again?’ ’’

Patrick and Warren have not had an especially close or long-lasting relationship, despite their shared Harvard ties and activity in progressive politics, sources close to each of them say.

But those close to both also say this: She owes much of her early success to him.

When Warren began her first Senate campaign, she benefited from the grass-roots political network that Patrick had built across Massachusetts. She inherited many of his top advisers, including Doug Rubin and Kyle Sullivan.

“He was instrumental. He was critical because he galvanized his organization around the state,’’ said Phil Johnston, a former Massachusetts Democratic Party chairman. “The field obviously is very important. And I think he helped her in many ways. If I were to point to one factor that was critical in her victory, it was that Deval really put his organization to work for her. At the time, that was a very powerful political force in Massachusetts.’’

Patrick also stepped in to help at a key moment, endorsing her at a time when she was attempting to fend off questions about her claims of Native American heritage. The governor had not planned to back a candidate that early — before Warren had won the Democratic primary — but he made a quickly arranged appearance at her campaign headquarters.

“I want to thank you so much, Elizabeth, for running,’’ he said, adding that he knows how rugged campaigning can be. “It’s a drag some days.’’

Later in the same event, when Warren faced a pointed question about whether her claims spoke to her “character’’ and “authenticity,’’ and her supporters in the room grew agitated, Patrick stepped forward to the microphone and took it on.

“First of all . . . the question is OK,’’ he said. “We have to project what we want in political discourse, right? And that means even when we don’t like the question, we gotta let it be asked.’’

“Second,’’ he continued, “Let me say on behalf of the people of the Commonwealth, we don’t care about that subject.’’

Warren, when pressed by reporters after Patrick finished speaking, declined to elaborate, saying, “I defer to the governor on this one.’’

After Warren was elected, she and Patrick overlapped during the last two years he was in office.

They worked on getting funding for the Green Line extension and protecting the state’s fishing economy. Both were in office during the Boston Marathon bombings, and have appeared together at news conferences, political events, and funerals.

Their relationship has grown warm but not chummy. There is no tension, and they’ve never had reason to be suspicious of or competitive with each other.

They may soon enough be debating each other, but no one can recall them disagreeing or getting in an argument.

They occasionally text, and about once a year they get together with their spouses for a meal. One year was in Cambridge, near Warren, and another year in Great Barrington, near Patrick’s vacation home in the Berkshires.

They both rose seemingly out of nowhere, catapulting from private lives into a top statewide elected office in a state where the political system has often rewarded those from connected families or who spend decades building a political career.

Each of them ran the kind of upstart, grass-roots campaign in Massachusetts that could play well in the living rooms of Iowa. They both have a talent for fiery rhetoric that could rile up a crowd at the Iowa State Fair, and both are already well-known in neighboring New Hampshire.

Their politics are both liberal, but Patrick, a former corporate counsel who is now an executive with Bain Capital, is more pro-business and she is more confrontational.

“There’s no doubt that Elizabeth is very much a champion of the populist wing of the Democratic Party. She has I think the virtue of being a woman. And that adds to the appeal,’’ Axelrod said. “It’s not clear to me how Deval would present himself in a race, but he clearly has a different style. . . . He’s someone who by nature is a pretty unifying figure.’’

One likely point of debate, should Patrick get in, is his ties to corporate America. He’s sat on boards of Coca-Cola and Ameriquest — connections that came up during his gubernatorial races — and since leaving office he has worked at Bain, a venture capital firm that came under attack when Mitt Romney, its former chief, entered politics.

“If Deval runs, I’m sure he’s going to have to place that experience in a context for people, because there will be those who will certainly try and use that against him,’’ Axelrod said. “What he’s doing at Bain, as I understand it, is social impact investing. There are a lot of good stories around that. But I’m pretty sure his opponents aren’t going to tell those stories, so it does become incumbent on him to do so.’’

Patrick has been having conversations and is soon planning to start campaigning for candidates in the midterms. If he were to run, he would have some catching up to do in building a fund-raising network and a national constituency. While Patrick helped Warren with his political network in Massachusetts, she has since built a national constituency — and donor list — that Patrick lacks.

“A lot of people contemplating running for president will be making the political calculus of who’s in and who’s out and who’s got what fund-raiser or what campaign manager,’’ said Tim Murray, who was lieutenant governor for much of the Patrick administration. “I don’t think any of that factors into Governor Patrick’s thinking on this. If he’s got a message in his heart and in his head, he’s going to get in regardless of who’s in or out.’’

Massachusetts Democrats will have their loyalties sorely tested if they wind up having two top-tier candidates from the state both vying for the nomination.

“It would be interesting. There’s never a dull moment in Massachusetts,’’ said Johnston, the former Massachusetts Democratic Party chairman. “Part of me feels like it’s a good thing. Just throw everybody out there and have as many of them run as possible, and let Democrats around the country decide which person would be the best to beat Trump. I don’t think anyone has a clear sense of that.’’

“If they both were to run, everybody will choose sides and we’ll see what happens.’’

Matt Viser can be reached at matt.viser@globe.com.