(NewsNation) — Vice President Kamala Harris is moving swiftly to secure Democratic delegates behind her White House campaign since President Joe Biden announced he won’t seek reelection and endorsed her.

Prominent Democratic elected officials, party leaders and political organizations have lined up behind Harris since Biden’s announcement Sunday. Still, there are plenty of Harris skeptics, and while she has secured endorsements across the party, big names like former President Barack Obama and former House Speaker Nancy Pelosi have not endorsed her as of Monday morning.

Dan Morain, author of “Kamala’s Way: An American Life,” said Monday on “Morning in America” that Harris can be “a very adept politician” but she’s often underestimated.

“She’s very quick on her feet. She was a prosecutor. She knows how to think quickly,” he said. “People underestimate her; they’ve always underestimated her. People who have underestimated her end up losing.”

Democrats are trying to put weeks of intraparty drama over Biden’s candidacy behind them. Biden’s departure frees up his delegates to vote for whomever they choose. Harris is thus far the only declared candidate.

There are two paths for replacing Biden at the top of the Democratic ticket. One is an “open” convention, a scenario the party hasn’t experienced since 1968.

On the first day of her presidential campaign, Harris brought in over $49.6 million in donations, her campaign confirmed to NewsNation.

Harris says she’ll do everything in her power to unite Democrats and the nation and defeat Trump.

NewsNation’s Andrew Dorn and the Associated Press contributed to this report.