WASHINGTON — Presidents get elected to run the nation. Some days that means knowing how to heal it.

For the first time since winning the White House, President Barack Obama faces such a moment Tuesday at Fort Hood. It his job to offer comfort, if not answers, after the shooting that left 13 people dead and 29 wounded on the bustling Texas Army post five days ago.

Obama will privately console families of those killed, and then publicly pay respects at a memorial service sure to be watched by American troops around the world. He and first lady Michelle Obama will also visit wounded troops in the hospital before returning to Washington.

This is Obama's time to take on healer role that can help shape a presidency at a time of national tragedy.

Obama's predecessor, George W. Bush, governed during the worst terrorist attack on American soil, the most crippling natural disaster in U.S. history, a space shuttle explosion, a shooting rampage at Virginia Tech, a tornado that wiped away a Kansas town, a bridge collapse in Minnesota, Midwestern flooding and California wildfires. Each response affected his standing, for better or worse, in a country that expects its president to be empathetic and clearly in charge.

History is full of other examples. Bill Clinton helped rebuild his troubled presidency with the way he reacted to the Oklahoma City bombings.

In this case, Obama has sought his own balance.

He has promised a full investigation of the Fort Hood shootings but has said little about it as police search for a motive. He has praised religious diversity in the military, trying to offer calm as questions loom about whether the alleged shooter had ties to extremist Islamic ideology. And he has delayed a trip to Asia to attend the memorial service.

The mass killing shook the nation even more because it happened in a presumed haven of U.S. security. The suspect himself is a soldier, Maj. Nidal Malik Hasan. Authorities say he fired off more than 100 rounds before a civilian police officer shot him. He survived and is in stable condition.

It wasn't even two weeks ago that Obama stood in the dark of night at Dover Air Force Base in Delaware, honoring the remains of 18 troops killed in Afghanistan. Now he will lead the mourning for 13 men and women who were working in the one place, as Obama put it, that "our soldiers ought to feel most safe."

Among those killed at Fort Hood were 21-year-old Pvt. Francheska Velez, who was pregnant and preparing to return home after a recent deployment in Iraq. And Spc. Jason Hunt, a 22-year-old who served in Iraq and was married two months ago. And Maj. Libardo Caraveo, 52, who was headed to the war zone in Afghanistan.