Updated 5:20 p.m. ET

A spokesman for Sen. Marco Rubio, the Florida Republican, told the Tampa Bay Times that his boss is looking for policy changes to keep guns out of the hands of criminals and the mentally ill.

"In the aftermath of the unspeakable tragedy in Newtown, Sen. Rubio, like millions of Americans, is looking for public policy changes that would prevent such a horrible event from happening again," spokesman Alex Conant said. "He remains a strong supporter of the Second Amendment right to safely and responsibly bear arms. But he has also always been open to measures that would keep guns out of the hands of criminals and the mentally ill. The challenge with gun laws is that by definition criminals do not follow the law. For example, Connecticut's gun laws, some of the strictest in the nation, were not able to prevent this atrocity. Nevertheless, he supports a serious and comprehensive study of our laws to find new and better ways to prevent any more mass shootings."

Update at 1:15 p.m.

Another pro-gun Democrat, Sen. Mark Warner of Virginia, who touts his "A" rating from the NRA, has called the Connecticut shooting a "game changer" and suggested new gun laws.

"I believe every American has Second Amendment rights, the ability to hunt is part of our culture," he told a CBS affiliate in Richmond, Virginia. " I've had a NRA (National Rifle Association) rating of an "A" but, you know, enough is enough," Sen. Warner said. "I think most of us, realize that there are ways to get to rational gun control. There are ways to grapple with the obvious challenges of mental illness."

Original Post at 10:01 a.m.

Senator Joe Manchin, D-W.V., has been as pro-gun, pro-NRA as anybody in Congress. During his 2010 re-election campaign, he famously demonstrated his opposition to the cap-and-trade bill by shooting the bill (literally) with a rifle .

Now in the wake of the Newtown massacre, Manchin says it is time to re-think gun control. As he said today on Morning Joe, "I don't know anyone that needs 30 rounds in a clip to go hunting …"

On Twitter, Manchin endorsed a proposal by Sen. Joe Lieberman to create a national commission on gun violence. But he said there must be action as an end result.

This awful massacre has changed where we go from here. Our conversation should move beyond dialogue.

- Senator Joe Manchin (@Sen_JoeManchin) December 17, 2012

Many gun control advocates have suggested immediately used it to call for new gun legislation.

President Obama has not yet specifically advocated new legislation to curb gun violence. But speaking in Connecticut Sunday night, he told the grieving families of Sandy Brook Elementary School. The president asked if the nation can say it is doing enough to protect its children.

"If we're honest with ourselves the answer is no," he answered. "We've not been doing enough. And we will have to change."

Obama has not made gun legislation a priority of his administration, although he supports renewing the assault weapons ban, which was in effect from 1994 until 2004.

Read more about calls for new gun legislation.

Watch the famous 2010 ad where Manchin, a Democrat, shot at climate change legislation: