"You can't pull up a quick text like 'National Security for Dummies,' " five-time Republican senator John Warner of Virginia said while attacking Republican nominee Donald Trump. He endorsed Democrat Hillary Clinton on Sept. 28. (Video: WUSA9 / Photo: Jahi Chikwendiu/The Washington Post)

When it comes time to pick a commander in chief, preparation is essential, retired senator John W. Warner of Virginia said Wednesday, explaining his decision to buck his party and endorse Hillary Clinton over Donald Trump.

“You can’t pull up a quick text like ‘National Security for Dummies,’ ” Warner, the maverick Republican, quipped at a news conference in Alexandria, where he was joined by Sen. Tim Kaine (Va.), Clinton’s running mate on the Democratic ticket.

Warner, 89, is a World War II veteran, a former U.S. Navy secretary and a former chairman of the Senate Armed Services Committee, and his comments focused heavily on military and national security issues.

He mixed war stories — literally, in some cases — with praise for Clinton and political jabs at Trump, a real estate executive, saying he felt compelled to share his thinking on the presidential race particularly for “those people still struggling with how to vote.” That included, he said, those in Virginia, a presidential battleground state.

With a backdrop of U.S. and Virginia flags, Warner recalled that during her days a junior senator from New York, Clinton came prepared to meetings that he led of the Armed Services Committee with papers “stuffed under her arms and dribbling onto the floor.”

When military witnesses appeared before the committee, Clinton was always “respectful,” Warner said, adding: “That’s one word that’s totally lacking from the other ticket.”

On foreign affairs, Clinton, a former secretary of state, has “a foundation of [her] own to build upon” as president, Warner said. “The other candidate, in my judgment, does not.”

Warner, who remained popular among his Virginia constituents throughout his five terms, said he’s been “distressed” by comments Trump has made about the state of the military and about military families.

“We have today the strongest military in the world,” Warner said. “No one can compare to us. … It is not in shambles. … No one should have the audacity to stand up and degrade the Purple Heart, degrade military families or talk about the military being in a state of disaster.”

After wrapping up at the lectern, he decided to return for one more shot at Trump, mentioning him by name for the first time. During his training in the Navy, Warner recalled, one lesson was “drilled into us.”

“Loose lips sink ships,” he said. “Got that Trump? Loose lips sink ships.”

Perhaps best known by some for marrying actress Elizabeth Taylor, Warner also has a history of parting ways with his party.

Warner famously opposed the Supreme Court nomination of Robert Bork, as well as the 1994 Senate candidacy of Oliver North of Iran-contra notoriety. He endorsed Democrat Mark R. Warner over Republican Jim Gilmore to fill his own seat in the U.S. Senate.

But until Wednesday, Warner had never endorsed a Democrat for president.

Both Kaine and Mark Warner, who was also on hand Wednesday, showered praise on the retired senator before he spoke — and recounted the ways their lives and political careers were intertwined in the state.

“He’s always put country and commonwealth above anything else,” said a beaming Kaine.