Hillary Clinton, the 2016 Democratic presidential nominee and former secretary of state, endorsed Joe Biden for president on Tuesday, during a virtual "Women's Town Hall" focusing on how women were responding to the COVID-19 pandemic. Saying she wanted to add her voice to "the many who have endorsed" Biden, Clinton said, "Just think of what a difference it would make right now if we had a president who not only listened to the science, put facts over fiction, but brought us together....Think of what it would mean if we had a real president, not just someone who plays one on TV."

Clinton teased her endorsement with a tweet Tuesday afternoon: "A little hint about who the surprise guest will be for @JoeBiden's 3pm ET town hall today: (She's excited.)"

A little hint about who the surprise guest will be for @JoeBiden's 3pm ET town hall today: (She's excited.) pic.twitter.com/iGHo6a6G1s — Hillary Clinton (@HillaryClinton) April 28, 2020

The endorsement comes after the end of a competitive Democratic primary. Clinton and Biden both faced their strongest challenges in 2016 and 2020 from the same candidate, progressive Bernie Sanders. This year, though, the infighting between the candidates ended earlier than in 2016 — Biden became the presumptive nominee more than two months earlier than Clinton did; Sanders continued to battle her for delegates into the summer.

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Clinton stayed off the 2020 campaign trail and publicly remained neutral during the primary, even though she confessed this winter she had remaining animus toward Sanders.

But both her presence and the history of her failed 2016 campaign at times loomed over Biden's campaign stops over the past year. Asked by a voter how he planned to beat Trump if he were the nominee, Biden turned his attention to the former secretary of state's campaign.

"Hillary is a really bright competent person—would've been a good president. But think about this: Do you know the detail of any of her plans? My guess is you're an informed voter and you probably don't unless you went online," Biden said in December in Exeter, New Hampshire. He stated Clinton's campaign chose more to confront Trump over his perceived personal faults, like his treatment of women, rather than focus on how her policies could help voters.

"I did 84 major events for Hillary Clinton all over the country, nobody campaigned for her more than I did," Biden noted.

Clinton's endorsement Tuesday could also provide an opportunity to smooth over any remaining tension between the competitive pair. Speculation about the two facing off for the 2016 Democratic nomination began in the summer of 2013, as a trip by Clinton to Biden's vice presidential mansion and to the White House to dine with President Barack Obama was seen as indication of her campaign plans.

As Clinton campaigned in the late summer of 2015, Biden was grieving the death of his son, Beau Biden, a family tragedy that he later cited as the reason did not challenge the former secretary of state for the Democratic nomination. "I believe we're out of time — the time necessary to mount a winning campaign for the nomination," Biden said with President Obama standing beside him.

But just days before the general election in October 2016, he told CNN "I thought I could beat Hillary. I thought I could beat anybody that ran," had he chosen to run.

It is uncertain how closely Clinton will be tied to Biden's campaign but her tangential connection could prompt replays of old hits from the president's re-election effort. Before the pandemic, Mr. Trump commonly name-checked her at his rallies and even the error page on his website still features a picture of Clinton behind podium with the presidential seal: "You're looking for something that doesn't exist..." the error message reads.

After news of Clinton's endorsement was announced, Trump campaign manager Brad Parscale said of Clinton and Biden in a statement, "Both of them carry the baggage of decades in the Washington swamp and both of them schemed to keep the Democrat nomination from Bernie Sanders."

Biden's new Clinton connection could also be perceived as a disadvantage for weary progressive voters, too, as shown when Michigan Representative Rashida Tlaib led a chorus of boos directed at Clinton during a Sanders event in February.

Jenna Gibson contributed to this report.