Washington (CNN) -- Before President Obama says a word during his Tuesday Oval Office address, the backdrop will make a statement for him: that he is the decider.
Obama is set to give his second Oval Office address, a speech meant to mark the end of combat missions in Iraq. But besides the remarks he will make, the setting of his speech will convey something, too.
"The Oval Office invokes the center of the presidential authority. That's the president's office, that's where he supposedly makes decisions, where he governs," says presidential historian Robert Dallek.
"[When] a talk to the nation is given from that office, [it] is underscoring his executive powers, his leadership."
The Oval Office symbolizes power, command, and authority, Dallek said. It shows the president, "as George W. Bush put it, is the 'decider' " and that symbolism is important.
For example, former President George H.W. Bush announced the start of the first Gulf war from the Oval Office, telling Americans and the world that he was the commander in chief just by setting the scene in the Oval Office.
And on the night of the terrorist attacks on September 11, 2001, former President George W. Bush spoke to the American people from the Oval Office, to show he was in command and to reassure the nation.
Dallek points out the differences between giving a speech in the Oval Office versus a speech in a different venue.
For example, Obama's speech in front of the joint session of Congress a year ago conveyed his desire to get Congress to act on health care reform.
"A joint session of Congress has a different function," Dallek said. A speech in front of both the Senate and House shows the president is "trying to convince Congress to join with him."
When Obama addressed both chambers in September 2009, the health care debate was still waging. He called for bipartisan proposals to address health care reform and focused attention on the issue, on Congress and on the presidency.
An Oval Office address is different. The prime-time address focuses the attention singularly on the subject matter.
"Presidents don't give speeches from the Oval Office casually," Dallek said. "It's given with forethought and consideration. So the fact that he's giving the current speech about the end of America's combat role in Iraq is something that he wishes to emphasize and underscore and in a sense I think it's a demonstration of his completion of his mission or fulfillment of a commitment that he made."
Because of the singular focus on the subject matter during Obama's Tuesday evening address, Obama will have to navigate the tricky road of marking the end of a war he did not support and honoring the lives of all the Americans killed in the war, Dallek said.
Obama must use a "certain amount of domestic diplomacy to bring the war to a close; you don't just end the war and say it's a mistake. It's unpalatable because of all the deaths," Dallek said.
So Obama must do it in a way that is "politically palatable to the American public -- that is at the heart" of his address Tuesday, Dallek said.
The Oval Office will also help convey a sense of intimacy of the message. Since former President Jimmy Carter, each president has delivered his farewell address from that room, using the office of the presidency to say goodbye to the American public.
President Reagan used the intimate space to comfort the public after space shuttle Challenger exploded in 1986.
President Johnson used the room in 1968 to tell Americans he would not seek re-election and President Nixon gave several speeches regarding the Watergate scandal, including his decision to resign from the presidency in the wake of Watergate in 1974.
Obama's other Oval Office address was two months ago to address the nation about the Gulf oil disaster.
And who does the presidential historian think was most successful at intimate talks to the American people?
Franklin Roosevelt's fireside addresses -- although there were no televisions at the time, these radio talks were effective in boosting the country's confidence.