In his first few weeks in office, sometime between celebratory bill signings and phone calls from foreign leaders, President Obama sat in the Oval Office for the most somber task of his presidency - penning letters to families of troops killed in combat.
The letter was signed "Barack," Ms. Merz told The Washington Times.
"Not 'president,' just his first name, and it just felt like, OK, my son has been acknowledged," she said.
Mr. Obama personalizes each letter, asking staffers to gather details about the service member, such as their hometown and where they were stationed, a White House aide said. The letters are sent to parents and spouses, and sometimes children of the fallen troops.
The president writes the notes by hand, then the letters are typed before he adds his signature.
Mr. Obama wrote the first few letters for troops who died in Iraq and Afghanistan while George W. Bush was president, and has written at least a dozen more since taking office.
The president told NBC News that the duty falls to him, though he did not initiate the wars and opposed the invasion of Iraq. In those moments of signing the letters, he said, "you realize every decision you make counts."
The White House declined to release any of the private letters or the names of families who received them, but The Times spoke with some who shared the contents of their letters.
Cpl. Brennan, 25, was supporting combat operations in Afghanistan's Farah province when he was killed last month.
Ms. Merz said the president's letter to her family in honor of her son was "lovely" and added, "It is meaningful to have Julian's death noted personally by him."
Six weeks before Cpl. Brennan was deployed, the Brooklyn resident married his fiancee to make sure she would have benefits if he was killed abroad.
Ms. Merz said she and her son often talked about national service. Like the president, she opposed the war in Iraq. As for Afghanistan, she described herself as ambivalent, but said that she and her son came to an agreement that "if our nation was going to engage in military action, everybody should serve."
As a parent of someone in combat, she realized, "I no longer have the privilege of saying I don't agree and not paying attention to what our nation was doing," she said.
Ms. Merz said she was struck by the personal tone of Mr. Obama's letter, which arrived before the official correspondence from Congress, and she wasn't sure whether they were his words or those of a staffer.
When told by The Times that Mr. Obama writes the letters himself, she said the words became more powerful.
"It says to me that he, too, will be paying attention to more than just the numbers, but the real stories," Ms. Merz said.
"One of the things I felt committed to even though I didn't agree with our military ventures was reading the names of the troops killed as they were listed," she said. "I just need to think about these people as individuals, and I hope that as a nation we are doing that and seeing them as real sons and daughters."
She added that Cpl. Brennan was "just beginning to grasp the real life of the Afghanis around him, feeling very committed to the human side of what was happening in Afghanistan and Iraq."
Their last conversation was on Inauguration Day, four days before Cpl. Brennan was killed by a roadside bomb. Both supported Mr. Obama's election, but they spoke that day about the Afghan people, she said.
Ms. Merz said she had been considering making the trip from New York to Washington for the inaugural festivities, but "I'm glad I didn't. I was home to get my son's call."
"I am so glad the president is trying to do the right thing personally in terms of families and the soldiers," she said. "He has a monumental task in front of him."
As Mr. Obama adjusts to the traditions bestowed upon the president as commander in chief, the duty is far different from saluting the Marine standing next to his Marine One helicopter or getting used to people standing when he walks into the room.
The president said on NBC News that the letters serve as a reminder - "that you've got hundreds of thousands of people - around the world who are putting themselves in harm's way and you are the commander in chief."
The White House said copies of the letters are preserved for historical archives.
The aide described the letters as "very gracious" but would not share the text because of the sensitive and personal nature of their content. The letters mention that the president appreciates the service member's sacrifice.
While serving as a U.S. senator, Mr. Obama would send families of Illinois service members condolence letters and an American flag that had flown over the Capitol.
Some he would call personally.
Mr. Bush also sent personal letters to the families of every one of the more than 4,000 troops who have died in the two wars, he told The Times in an interview last year. He said he leaned on his wife, Laura, for support in the gut-wrenching task.
Mr. Bush also met privately with more than 500 families of troops killed in action and with more than 950 wounded veterans, said Carlton Carroll, a White House spokesman during the Bush administration.
"Everything you do matters," Mr. Obama told Fox News a few days after the NBC interview. "I'm now signing letters to the families of troops who have fallen in Iraq or Afghanistan.
"Every time you sign that, you are reminded that you have enormous responsibilities and so, that's why all of these debates - when I'm talking to Democrats or Republicans, one of the things I try to remind them and something I remind myself every single day is the only criteria for what I do should be - is it working for the American people?
"Because this job is too big, too important, to just want to occupy space," he said. "And if I've spent the next four years, every day, making decisions based on that single criteria, is this going to help the American people achieve their dreams and keep them safe, then I'll be able to look at myself in the mirror and say, 'You know what, you did a good job.' "