President Obama moved Thursday to put the muscle of the White House and his network of supporters behind a gun control package tracking toward the Senate floor, calling on voters to pressure Congress into backing it as the proposal runs into resistance on Capitol Hill.

The president, in a set of brief remarks from the White House Thursday surrounded by the mothers of shooting victims, raised concern that the shock from the Newtown elementary school shooting could soon fade.

“Less than 100 days ago that happened. … Shame on us if we’ve forgotten,” Obama said. “I haven’t forgotten those kids. Shame on us if we’ve forgotten.”

Amid signals from Washington that the Senate bill could be losing momentum and high-dollar ad campaigns on both sides, the president was there to deliver a message to wavering lawmakers. “Don’t get squishy,” he said.

Obama, accusing opponents of drumming up “fear,” urged supporters to call members of Congress and pressure them into backing the package.

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