Joe Biden’s presidential campaign on Wednesday began privately deliberating whether to formally request Secret Service protection for the candidate, according to a person with knowledge of the situation, a day after protesters rushed the stage at his event in Los Angeles in what experts called a major security breach.

Both Biden and fellow candidate Sen. Bernie Sanders (I-Vt.) rely on private security firms to handle their public appearances, which is unusual this late in a presidential campaign cycle in comparison with 2016, 2012 and 2008. But their emergence over the past week as the clear front-runners in the Democratic primaries has prompted calls for the Department of Homeland Security, which oversees the U.S. Secret Service, to authorize full-time protection for both of them.

“Taking into consideration the remaining candidates’ large campaign operations, high polling averages, as well as physical threats to their safety … I urge you to immediately initiate the consultation process to determine whether to provide USSS protection” to Biden and Sanders, Rep. Bennie Thompson (D-Miss), the chairman of the House Homeland Security Committee, wrote in a letter Wednesday to acting DHS secretary Chad Wolf.

Rep. Cedric L. Richmond (D-La.), a member of the Homeland Security Committee and co-chair of Biden’s campaign, told reporters that Democratic lawmakers were “worried about” security for the Democrats on the campaign trail even before the incident at Biden’s speech on Super Tuesday.

The Biden campaign has begun deliberating over whether to move forward with a formal request to the Secret Service, according to the person familiar with the situation, who spoke on the condition of anonymity to comment freely about a sensitive security matter. The Sanders campaign did not immediately respond to questions on the subject. The DHS also did not respond to a request for comment.

The onstage skirmish during the former vice president’s remarks in Los Angeles highlighted the potential risks for candidates addressing large crowds. A pair of vegan activists holding signs reading “Let Dairy Die” rushed the stage before being physically pushed and pulled away by bystanders including Biden’s wife, Jill, and a campaign aide in a video that has circulated widely online.

The incident was a “massive security failure,” said Jonathan Wackrow, a risk-management consultant at Teneo who served as a Secret Service agent in the agency’s Presidential Protective Division. “These were environmental activists. Anyone aligning with a specific ideology is potentially dangerous. I think both Bernie and Biden would want it at this point.”

The question over which presidential candidates deserve taxpayer-funded Secret Service protection, and when such protection should begin, can be a tricky calculation — for federal officials and the candidates themselves. Under federal guidelines, a candidate must meet minimum standards that include being a “major” candidate in his or her party — generally defined as a someone who is regularly appearing at rallies, conducting a national campaign and receiving at least 15 percent support in established polls. Biden and Sanders both meet such requirements.

Campaigns must request protection from the DHS, and a bipartisan congressional advisory committee — led by the Senate majority leader, currently Sen. Mitch McConnell (R-Ky.) — helps review the request before the DHS secretary makes a decision.

Outsourcing security to the federal government can be a boon for cash-strapped campaigns and also bestow a heightened legitimacy on candidates. But some candidates in past presidential campaign cycles have tried to hold off over concerns that a large security entourage could hamper their ability to interact more directly with supporters.

Both Biden, during his eight years as vice president, and Sanders, during his 2016 contest against Hillary Clinton for the Democratic presidential nomination, have received Secret Service protection in the past.

“Bernie Sanders and Joe Biden need secret service protection,” Robert Gibbs, a White House press secretary under President Barack Obama, said on MSNBC on Tuesday. Of the skirmish at Biden’s event, he added: “What happened tonight was nothing short of genuinely scary. … They should have Secret Service protection in the next 24 to 48 hours.”

Obama received Secret Service protection earlier than any other candidate — in May 2007, nearly a year and a half before the 2008 election. The congressional advisory committee at the time warned that the first viable African American candidate for the White House faced an unusually high security risk. (Hillary Clinton, who also was running for the Democratic nomination at the time, already received Service protection in her capacity as a former first lady.)

In 2012, the eventual Republican nominee, Mitt Romney, got protection in February of that year, while Donald Trump and Ben Carson, running for the GOP nomination in the 2016 cycle, began receiving Secret Service coverage in November 2015.

In 2016, Trump and Clinton had instances at their campaign events in which Secret Service agents jumped onstage to surround them over concerns about protesters.

As president, Trump receives round-the-clock protection. Former presidents continue to have a smaller Secret Service details — but Biden no longer is granted such protections as a former vice president.

Wackrow, the former agent, has not seen intelligence reports about the 2020 candidates. But he suggested Biden’s threat profile might be magnified because of President Trump’s unfounded allegations that the former vice president had acted improperly when his son Hunter Biden served on the board of a Ukrainian energy company.

That accusation led Trump last summer to privately pressure Ukraine’s president to open an investigation into the Bidens, a demand that ultimately led House Democrats to impeach Trump. The president has berated the Bidens in public remarks and called on China to open an investigation into Hunter Biden’s business activities in that country.

“They’ve now made him a target,” Wackrow said. “It’s all rhetoric, but rhetoric can transcend to physical harm.”

Matt Viser, Cleve R. Wootson Jr. and Sean Sullivan contributed to this report.