For years, the Secret Service has meted out its limited protection resources based on the person the agency was protecting. The sitting president and vice president are assigned the highest amount of protection. Former presidents, major-party candidates and visiting dignitaries receive less.

Former President Donald J. Trump broke the mold for shaping protective details when he left office in 2021, because he maintained an intense schedule that demanded a suite of protection not previously seen for former commanders in chief.

The Secret Service would not disclose the exact number of agents and different types of protective resources assigned to the around 40 people it currently protects. But the attempted assassination of Mr. Trump in Butler, Pa., and another on Sunday at his golf course in West Palm Beach, Fla., have forced a reckoning of the longtime model and its relevance in today’s threat environment.

This is what we know about how the Secret Service guards its protectees.

The sitting president and vice president are always the highest priority for protection resources.

That is because the Secret Service’s priority is to protect the continuity of government — in other words, to keep the president and the vice president safe so that they can run the country. This is why they will always get the most assets, from personnel to technology, assigned to them.

While the president always has a Secret Service countersniper — an agent trained to take out an assassin who has a gun — assigned to his protection, that has not always been the case for the vice president, according to a former official with knowledge of the process who spoke on the condition of anonymity to discuss sensitive matters.

There are notable differences in assets assigned to the president and the vice president, as well. By law the Defense Department must provide certain resources to help the Secret Service protect the president, such as aircraft to transport the president and security equipment. That requirement is not established in law for the vice president or others under Secret Service protection.

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