The protests had turned into riots.

Two days after a police officer murdered George Floyd by kneeling on his neck, the mayor of Minneapolis called the governor, Tim Walz, asking for help. The police had lost control of the situation. The city needed the Minnesota National Guard.

That same Wednesday evening, May 27, 2020, the city’s police chief, Medaria Arradondo, sent an email to the state commissioner of public safety conveying a similar message, asking the National Guard for “immediate assistance with significant civil unrest.” He said 600 troops were needed.

It was not until that Thursday afternoon that Mr. Walz, a Democrat, signed an executive order activating the Guard. That night, before large numbers of troops were deployed, rioters set a police station on fire. And it took until Saturday, five days after Mr. Floyd had died and three days after Mayor Jacob Frey of Minneapolis had requested National Guard assistance, for the situation to begin to calm.

Ever since, the governor’s response to those requests has been under scrutiny, even more so now that Vice President Kamala Harris has selected Mr. Walz as her running mate.

Mr. Walz, a National Guard veteran, was in charge when his state became the center of a searing discussion about racism and police violence, and as it experienced some of the country’s worst unrest in a generation.

In that moment, he had to decide whether and how to use the military, providing insight into how he might perform during a global crisis as vice president or, possibly, as president and commander in chief.

A series of official reports about that week found failures at all levels of government, including some on the governor’s part.

Mr. Walz has said little recently about his response, and he declined to be interviewed for this article. But a reconstruction of the days after Mr. Floyd’s murder reveals that Mr. Walz did not immediately anticipate how widespread and violent the riots would become and did not mobilize the Guard when first asked to do so. Interviews, documents and public statements also show that, as the violence increased, Mr. Walz moved to take command of the response, flooding Minneapolis with state personnel who helped restore order.

MONDAY, MAY 25 — WEDNESDAY, MAY 27

George Floyd Is Murdered

In 2020, Mr. Walz, a former high school teacher and congressman, was just over a year into his tenure as governor when Covid-19 began spreading widely in the United States. Like many governors, he shut down schools and required certain businesses to close. He told residents to stay home.

“These last few weeks have been difficult, but it’s only going to get harder,” Mr. Walz said in his April 2020 state of the state address, which he delivered virtually from home. “Long hours of darkness