Casey's attendance is notable; the moderate senator had previously been a strong supporter of gun rights but said the shooting in Newtwon, Conn., changed his thinking. He has since called for tighter gun controls.
Later in the week, Obama will posthumously award the Presidential Citizens Medal to the six teachers and administrators who died in December's elementary school shooting.
Obama is also expected to repeat his call for stronger gun controls in his State of the Union address on Tuesday.
A Quinnipiac University poll released Thursday suggested the president's gun-control plans could be resonating, with 92 percent of all voters saying they support requiring universal background checks on gun purchases. That total includes 89 percent of Republicans, 92 percent of independents and 96 percent of Democrats.
The poll also found sizable support for other aspects of the gun-control plan presented by the president. A majority of voters support a ban on the sale of assault weapons (56-39 percent) and high capacity magazines (56-40 percent).