Broward County educators and advocates saw Mr. Rubio’s letter as an indictment of a program called Promise, which the county instituted in 2013 — one year before the Obama guidance was issued — and has guided its discipline reforms to reduce student-based arrests in Broward County, where Stoneman Douglas is.

The N.A.A.C.P. said that Mr. Rubio “notably backs away from raising the purchase age for assault-style rifles and restricting magazine capacity,” and instead focuses on a system that once sent one million minority students to Florida jails for “simple and routine discipline issues ranging from talking back to teachers to schoolyard scuffles.”

The program was praised by former Secretary of Education Arne Duncan, and echoes the goals of the 2014 Obama guidance in discouraging schools from using law enforcement as a first line of defense for low-level offenses.

In the days before making his request, Mr. Rubio released a proposal that he said would remedy lapses in the Promise program and the 2014 guidance.

In a tweet on Tuesday, Mr. Rubio noted that the gunman was not in the Promise program, but had displayed violent and threatening behavior.

“The more we learn, the more it appears the problem is not the program or the DOE guidance itself, but the way it is being applied,” Mr. Rubio said, referring to the Education Department. “It may have created a culture discourages referral to law enforcement even in egregious cases like the #Parkland shooter.”

Long before the attack in Parkland, Fla., the 2014 discipline guidelines, which encouraged schools to examine their discipline disparities and to take stock of discriminatory policies, were already on Ms. DeVos’s radar — but not because they were seen as a possible culprit in the next school shooting. Conservatives were using the Trump administration’s effort to rein in federal overreach to reverse policies designed to protect against what the Obama administration had seen as discriminatory practices.