President Obama will observe a moment of silence at 9:30 a.m. today at the White House, marking one week since a lone gunman opened fire in a Connecticut elementary school, killing 20 first graders before turning a gun on himself.

And he'll issue a video response to the "We The People" petitions that have been submitted to the White House in the wake of the Newtown tragedy, urging viewers to call Congress "as many times as it takes" to push for gun restrictions. He earlier this week called on Congress to ban the sale of military-style assault weapons and high-capacity ammunition clips as he announced that Vice President Joe Biden would lead an effort to develop "concrete proposals" to stem gun violence.

"If we're going to succeed it's going to take a sustained effort," Obama says in the video. "You started something and now I'm asking you to keep at it."

Petitions relating to gun violence have amassed more than 400,000 signatures, making it one of the most popular petition issues since the White House launched We the People. One of the gun petitions was the fastest petition ever to reach the 25,000 signature threshold required for White House review.