President Donald Trump on Monday expressed the nation's "boundless" gratitude for the ultimate sacrifice paid by Americans defending the United States, dedicating his first Memorial Day address as commander in chief to a top Cabinet secretary and two other families who lost loved ones.

Participating in the somber, annual observance at Arlington National Cemetery, Trump recounted the stories of Green Beret Capt. Andrew D. Byers of Colorado Springs and Christopher D. Horton of the Oklahoma National Guard as Byers' tearful parents and Horton's emotional widow looked on.

Trump also singled out for special mention Homeland Security Secretary John Kelly, a retired Marine four-star general whose son, Marine 2nd Lt. Robert M. Kelly, was killed in November 2010 after he stepped on a land mine while on patrol in southern Afghanistan.

To all Gold Star families, Trump said of their lost service members: "They each had their own names, their own stories, their own beautiful dreams. But they were all angels sent to us by God and they all share one title in common and that is the title of hero, real heroes."

"Though they were here only a brief time before God called them home, their legacy will endure forever," Trump said.

Horton, a sniper sent to Afghanistan in 2011, died in a gun battle with the Taliban near the Pakistan border three months into his deployment. Byers was on his third combat tour and, Trump said, ran through smoke and a hail of bullets to rescue an Afghan soldier when he was killed last November.

Secretary Kelly's other son, Johnny, is getting ready for his fifth military deployment. A son-in-law, Jake, is a wounded warrior.

Trump also recognized former U.S. senator and GOP presidential nominee Bob Dole, 93, who suffered lifelong injuries during World War II. He attended the ceremony along with his wife, Elizabeth Dole, also a former U.S. senator.

"As we honor the brave warriors who gave their lives for ours, spending their last moments on this earth in defense of this country and of its people, words cannot measure the depth of their devotion, the purity of their love or the totality of their courage," Trump said.

"We only hope that every day we can prove worthy not only of their sacrifice and service, but of the sacrifice made by the families and loved ones they left behind. Special, special people," he said.

Before the remarks, Trump laid a wreath at the Tomb of the Unknown Soldier, touching it for a long moment before stepping away. He then rested his hand on his heart as a bugler played "Taps."

Stepping to the microphone to deliver the address, Trump seemed to relish the warm welcome from the audience gathered in the sun-splashed amphitheater. Trump has been feeling particularly aggrieved in recent weeks by federal and congressional investigations into contacts between his associates and Russian government officials, including news reports that Jared Kushner, his son-in-law and top White House adviser, proposed establishing secret back-channel communications with Russia during the presidential transition.

The president was accompanied to Arlington cemetery by Vice President Mike Pence, Defense Secretary Jim Mattis and Gen. Joseph Dunford, chairman of the Joint Chiefs of Staff, as well as a slew of advisers and Cabinet members, including veterans' secretary David Shulkin and housing secretary Ben Carson.

After the address, Trump visited a section of the cemetery for U.S. service members killed in the Iraq and Afghanistan wars. The White House said Trump visited the gravesite of Robert Kelly, who was laid to rest in Section 60.

Asked what meaning Memorial Day held for him, Secretary Kelly said: "Sad."

Accompanied by Pence, Trump walked briefly among the white marble headstones and greeted families, including Brittany Jacobs and her 6-year-old son, Christian, who was dressed like a Marine. Jacobs' father, Marine Sgt. Christopher Jacobs, died during a training accident in California in 2011.

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