WASHINGTON (AP) — Topless demonstrators crashed a Bernie Sanders rally in Nevada two weeks ago. On Tuesday, two animal rights activists rushed the stage where Joe Biden was giving a victory speech after a stunning primary triumph, and they were carried off, protest signs flailing.

Armed and seriously dangerous threats these individuals were not. But the breaches were concerning enough to prompt an online outcry that the Democratic presidential candidates be granted protection by the U.S. Secret Service. That demanded was followed by a letter Wednesday from some House Democrats advocating more urgent action.

None of the Democratic candidates is yet under the protection of the Secret Service, in part because not one of the the major contenders has formally asked for it. A request generally triggers the agency's assessment of whether to provide protection to candidates, according to two people familiar with the matter who spoke to The Associated Press on condition of anonymity. The people were not authorized to publicly discuss the issue.

The leading candidates in 2012 and 2016 all had Secret Service protection at this point in those races. Sanders, a Vermont senator, and Biden, a former vice president, emerged as front runners following Tuesday's primaries.

The Secret Service protects, by statute, the president and vice president and their families, as well as some other senior government officials. It is also authorized to provide protection to major party presidential candidates, an authority granted after the assassination of Robert F. Kennedy in 1968.

Biden, code-named “Celtic,” had Secret Service protection from the time he was selected as Barack Obama's running mate through about six months after his term as vice president expired. Unlike presidents, the protection of former vice presidents does not last for life.

Sanders, code-named "Intrepid," was granted Secret Service protection in February 2016. It ceased not long after he ended his presidential bid.

The process for assigning a security detail to a candidate generally requires that campaigns initiate the request for protection. The Secret Service does a threat assessment and consults with Homeland Security officials and a congressional commission made up of the majority and minority leaders of both chambers, plus another member. The ultimate decision on whether or not to provide protection is made by the Department of Homeland Security.

Biden could be provided a temporary detail under the law because of his status as a former vice president; that call is made at the discretion of the homeland security secretary.

The Sanders campaign says it does not comment on security measures of any kind.

Some campaigns can be resistant to requesting protective details because of the additional logistical and planning constraints put on by the Secret Service's security requirements.

Rep. Cedric Richmond, D-La., said Wednesday that the House Homeland Security Committee has asked the Secret Service to provide protection to all remaining major presidential candidates.

Richmond, one of Biden’s campaign co-chairmen, said members of Congress were “very worried” about the incident Tuesday night, when two protesters made it within feet of Biden. Biden's wife, Jill, and several staff members, including one trained security officer employed by the campaign, physically restrained the women and carried them from the stage before they reached Biden.

Last month in Nevada, a woman climbed the stage during a Sanders rally, stripped off her top and grabbed a microphone before she was removed from the stage. A second Sanders rally in California not long after was also disrupted by animal rights activists.

The guidelines about protection "set forth a number of discretionary factors that may be considered when deciding whether to authorize USSS protection for a major candidate, reflecting the scale and seriousness of the candidate's campaign,” the chairman of the House committee, Rep. Bennie Thompson, D-Miss., wrote acting DHS Secretary Chad Wolf and members of the congressional advisory committee on Wednesday.

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Associated Press writers Bill Barrow in Los Angeles and Will Weissert in Washington contributed to this report.