In her farewell speech at the National Press Club in Washington today, Homeland Security Secretary Janet Napolitano said the “key to success” during her four and a half years leading the DHS has been shaping a department that’s “flexible and agile.”

“Being flexible and agile means acknowledging that we may not be able to stop all threats all the time, but we can and must be prepared to address them quickly when they happen, minimize their consequences, draw pragmatic lessons and emerge stronger and better,” she said. “These are the most critical elements of our ability to meet our complex mission. And I believe we are seeing that approach bear fruit in a profound, positive way.”

Napolitano is leaving the department to head the University of California without a successor in place.

She hailed her “see something, say something” program, which D.C. commuters are periodically reminded of in a booming Napolitano voice ringing across the Metro platforms. The secretary said she expanded the campaign “to more than 250 states, cities, transportation systems, universities and private sector entities nationwide to encourage the public to play an active role in reporting suspicious activity.”

Napolitano also praised her shift in immigration enforcement to focus on “criminals, national security and public safety threats, repeat offenders, and egregious immigration violators.”

“Over the past four and a half years, we have invested historic resources to prevent illegal cross-border activity area, and because of these investments and manpower, and technology, and infrastructure our borders are now better staffed and better protected than at any time in our nations history. It illegal crossings have dropped to near 40-year lows,” she said.

“…We instructed our immigration agents and officers to use their discretion, under current law, to not pursue low priority immigration cases like children brought to the United States illegally by their parents. Children brought here through no fault of their own and you know no other country as their home.”

That was necessary, she said, because “Congress had a chance to give the so-called dreamers a way to stay in our country through the DREAM Act but, unfortunately, that legislation failed to garner the 60 votes need for cloture, falling just five votes short despite strong bipartisan support.”

“So, in June of last year, I used my prosecutorial discretion to create Deferred Action for Childhood Arrivals, DACA, a process that gives young people who meet the strict criteria a two year provisional legal status to remain in the United States. In just its first year, over half a million individuals have requested deferred action. And after a thorough review of each of those cases, including a background check, 430,000 requests have already been approved, allowing these young people to continue to contribute to the country they call home,” Napolitano continued.

“DACA, of course, is no substitute for comprehensive immigration reform, which is the only way to face the long-standing problems with our immigration system. But, it is indicative of our larger approach, to devote historic resources to the border, reorient our enforcement priorities, and build more flexibility into the system.”

As she leaves, Napolitano said, “many things still need tending.”

In an “open letter” to her successor, she advised confronting all threats, forging strong relationships with U.S. partners and Congress, and supporting expedited traveler programs.

“You will need to continue to ensure the security of key government leaders and events of national significance,” she continued. “…You will also have to prepare for the increasing likelihood of more weather-related events of a more severe nature as a result of climate change and continue to build the capacity to respond to potential disasters in far-flung regions of the country that could occur at the same time.”

“…You will need a large bottle of Advil.”