Obama's appearance at an interfaith vigil in the once-tranquil town of Newtown will be watched closely for clues as to what he meant when he called for "meaningful action" to prevent such tragedies in the wake of the massacre on Friday.
But politics will take a back seat to grieving, as more details emerge about the 12 girls, eight boys and six adult women that gunman Adam Lanza killed at the Sandy Hook Elementary School before killing himself.
Olivia Engel had a part in a nativity play at St. Rose of Lima Catholic Church. "She was supposed to be an angel in the play. Now she's an angel up in heaven," Monsignor Robert Weiss told a standing-room-only crowd at the church before the play on Saturday.
Emilie Parker, another of the child victims, was studying Portuguese with her father. A Facebook memorial page for her already had nearly 147,000 "likes" as of Saturday night.
Vicki Leigh Soto, 27, saved her first-grade students' lives by putting herself between the kids and the gunman. Britain's Independent on Sunday newspaper splashed her photo on its front page with the caption "The Heroine of Sandy Hook."
School district officials said classes would resume Tuesday, except for Sandy Hook - as of Saturday night, they were still working on a plan for how and where to let the school's kindergarten-through-4th-grade classes resume.
STILL LOOKING FOR ANSWERS
Obama plans to travel to the affluent town of 27,000 people about 80 miles (129 km) from New York City to meet with victims' families and speak at the vigil at 7 p.m. local time (0000 GMT on Monday).
Though Americans have seen many mass shootings in the past decades, the victims have rarely been so young. On Saturday, some Democratic lawmakers called for sweeping new gun-control measures, a move certain to run up against stiff opposition from the nation's powerful pro-gun lobby.
While the president and families mourn, police are still pushing for a fuller explanation of what drove Lanza, 20, to apparently kill his mother at her house, go to Sandy Hook Elementary, shoot out a window and storm through the school with multiple weapons.
Police earlier said they had assembled "some very good evidence" on the killer's motives.
He had struggled at times to fit into the community and his mother Nancy pulled him out of school for several years, to home-school him, said Louise Tambascio, the owner of My Place Restaurant, where his mother was a long-time patron.
Nancy Lanza legally owned a Sig Sauer and a Glock, both handguns commonly used by police, and a military-style Bushmaster .223 M4 carbine, according to law enforcement officials, who also said they believed Adam Lanza used at least some of those weapons.
His father issued a statement saying the family was in a "state of disbelief."
The death toll exceeded that of one of the most notorious U.S. school shootings, the 1999 rampage at Columbine High School in Littleton, Colorado, where two teenagers killed 13 students and staff before fatally shooting themselves.
At Virginia Tech, a Blacksburg, Virginia university where in 2007 a gunman killed 32 people in the deadliest school shooting in U.S. history, an announcer extended sympathies to the residents of Newtown before a basketball game on Saturday.
(Additional reporting by Dan Burns, Edward Krudy, Edith Honan, Chris Kaufman, Dave Gregorio, Colleen Jenkins, Martinne Geller and Chris Francescani; Writing by Ben Berkowitz; Editing by Paul Simao)