Biden, "talked about Elizabeth Warren frequently, unprompted," Ward told Powerhouse Politics podcast hosts, ABC News' Political Director Rick Klein and Chief White House and Washington Correspondent Jonathan Karl, when he recounted interviewing Biden about issues that split the Democratic party.
In the early 2000s, Warren had critiqued Biden for his support of legislation that made it harder for consumers to declare bankruptcy.
"So she framed it as him basically attacking women at the behest of large corporations back when she was a Harvard professor -- and that was obviously still sticking in his craw," Ward said.
Ward's new book explores the fraught relationship between former President Jimmy Carter and former Sen. Ted Kennedy and the challenge from within the Democratic party that threatened to unseat a sitting president.
Ward described Biden as in the "more Carter wing, which is the more moderate wing," of the Democratic party, and the tensions between Warren and Biden could resurface if Biden chooses to face off against Warren in the 2020 presidential race.
As of now, the race will be difficult for many.
Ward said "the door is slightly ajar" for Trump to lose ground to a Republican primary challenger.
"That's not a huge opening," Ward said. "But I think up until now the ground has been sort of tilled a little bit for Trump to actually lose some real support. He's not there yet, but he has been softened up. This shutdown thing has been sort of like a few jabs that have hurt him in a way that he's kind of not been hurt with his base up to this point."
In an ABC News/Washington Post poll, 53 percent of people surveyed blamed Trump and the Congressional Republicans for the shutdown.
Ward's predictions for which Republicans could potentially topple Trump: former U.N. Ambassador Nikki Haley or Sen. Marco Rubio, R-Fla.
"The thing about Nikki Haley is she served under his administration," Ward told Powerhouse Politics. "And she could come in and say, 'I served under this president. I love him and respect him but I feel like he's not going to win. The Republican party needs somebody else,'" Ward said.
"Otherwise you're going to get all these Trump voters who feel like the 'Never Trump'-candidate is attacking them personally because that's how politics works in the era of tribalism, especially in the area of Trump. Trump voters feel like, 'Oh you're criticizing Trump? You're criticizing me.'"
With more and more Democrats joining the race, none have appeared to take the lead yet. When asked an open-ended question about whom they would supporting in a primary or caucus today, 43 percent of Democrats and Democratic-leaning independents have no opinion, an ABC News/Washington Post poll found.
"Obviously the energy in the Democratic Party is on the left," Ward said. "Most of the Democratic candidates for president seem to be in that wing."
Ward's book details the historically-tense relationship between Carter and Kennedy, including "the most humiliating and embarrassing moment of Jimmy Carter's life," according to Ward.
On the stage of the 1980 Democratic convention, Carter's wish was to get a photo with Kennedy with their hands raised in the air together.
"Kennedy finally gets there and the place goes nuts," Ward recalled. "And so he goes up and shakes hands with Carter but won't do the hands in the air thing. And Carter keeps at it for like five, six minutes. Kennedy circulates the stage, he goes around shakes hands with everybody. Carter shakes hands with him like three or four more times and one time he actually gets him close," Ward said.
"And Kennedy won’t do it."
Carter, "actually did defeat the giant," Ward said. "He did beat Ted Kennedy. But I think in large part because of what happened, on the stage at that final night, I think he just came out of the convention looking pathetic."
Over the years, though, Ward said, Carter has let go of some of his animosity toward Kennedy.
"He still blames Kennedy," Ward said. "But I think he has mellowed in his vitriol towards him for running against him."
Every Wednesday, ABC Radio and iTunes bring you the Powerhouse Politics Podcast which includes headliner interviews and in-depth looks at the people and events shaping U.S. politics. Hosted by ABC News' Chief White House Correspondent Jonathan Karl and ABC News Political Director Rick Klein.