President Obama's historic plunge Wednesday into the politics and realities of gun control in America has mobilized advocates on both sides of the issue.

But though his major proposals, from banning assault rifles to more stringent background checks and ammunition limits, are being rolled out in the shadow of the school massacre in Newtown, Conn., their Capitol Hill prospects remain highly uncertain given long-standing resistance to such efforts.

Both Obama and Vice President Biden, head of the president's task force on gun violence, said as much during their televised announcement of the gun violence prevention initiative.

"I have no illusions about what we're up against or how hard the task is in front of us," Biden said. "But I also have never seen the nation's conscience so shaken [as] by what happened at Sandy Hook."

Said Obama, nodding to the reality of politics, pundits, and politicians: "This will be difficult."

The powerful National Rifle Association unveiled its own campaign in advance of Obama's, referring to him as an " elitist hypocrite" in an online video that also noted that there are armed guards at the school the president's daughters attend.

Obama acknowledged that action he plans to take through his executive power s — including ending the freeze on federal spending on gun violence research and attention to mental health issues — is "no way a substitute for action from Congress."

"Congress must act, and Congress must act soon," he said, adding that "this will not happen unless the American people demand it."

Obama said his administration will not propose any action to reduce the number of weapons, estimated at around 300 million, already in circulation in the U.S, or address existing troves of high-capacity magazines.

The White House also stayed away from proposing purchase waiting periods or federal gun licensing or registration requirements that in the past have generated heated opposition from those who oppose controls on guns.

"The gun policy package that President Obama announced today shows his genuine respect for the Second Amendment rights of law abiding Americans," said Jonathan Cowan, head of the Third Way, a center-left think tank, in a statement. "But it also makes clear that the Second Amendment does not extend to terrorists, criminals, or the severely mentally ill, and it does not apply to weapons of warfare."

House Judiciary Chairman Bob Goodlatte, a Virginia Republican, said, however, that "good intentions do not necessarily make good laws" and that any action must not "trample on the rights of law-abiding citizens to exercise their constitutionally guaranteed rights."

The White House announced that the president will immediately initiate 23 executive actions, including incentives to help schools hire "resource officers" and nominating a top federal prosecutor to fill the long-vacant position of director of the Bureau of Alcohol, Tobacco, Firearms and Explosives.

But, again, the tough, polarizing issues are the ones that the highly polarized Congress — and one where the GOP-controlled House will wait for action first from the Democratic-controlled Senate — has to consider.

Depending on where you sit, Obama's push is either a common-sense strategy to keep high-powered guns out of criminals' hands or an executive power grab that seeks to restrict a constitutional right.

Proposals That Require Congressional Action:

1) Requiring Background Checks For All Gun Sales

This action would close the so-called gun show loophole that exempts private gun sellers from running criminal checks on their prospective buyers. Current law requires that only licensed firearms dealers screen buyers through the National Instant Criminal Background System.

An estimated 40 percent of gun sales take place in that private sector space, including gun shows, pawn shops and flea markets, the administration says.

The White House rationale: The checks over 14 years have "helped keep more than 1.5 million guns out of the wrong hands," including felons and those convicted of domestic violence.

Of the tough-to-pass gun measures, this appears to be the one that has the best chance to advance, and a Pew poll this week found overwhelming and bipartisan backing for the change.

2) Reinstate And Strengthen Ban On "Military Style" Assault Weapons

The proposal is similar to the ban in place in the U.S. between 1994 and 2004. The White House argues that after Congress allowed the ban to expire, more than a third of police departments reported an increase in their use by criminals.

Obama is not proposing specific legislation, but his aides say the White House is working with Senate and House leaders on the issue, including California Democratic Sen. Dianne Feinstein, who has been pushing a renewal of the assault weapons ban.

Feinstein, author of the now expired 1994 assault weapons ban, said in a statement: "Next week, Senate and House cosponsors will introduce legislation to prohibit the sale, transfer, manufacture and importation of assault weapons and high-capacity ammunition feeding devices that carry more than 10 rounds. I hope that [Senate Judiciary Committee] Chairman [Patrick] Leahy [D-Vt.] will hold hearings on this bill in the Judiciary Committee as soon as possible."

Senate Majority Leader Harry Reid, D-Nev., however, in a recent interview with National Journal, already suggested that he and his fellow Democrats pursue a "careful and cautious" course on gun control.

The Senate, whose agenda he controls, should focus on legislation "that we know we can do," Reid told the publication this week.

3) Limit High-Capacity Magazines To 10 Rounds

If passed, this would reimpose the high-capacity magazine limit to the level included in the 1994 assault weapons ban.

Though most of the gun violence and related deaths in the U.S. are caused by individuals using handguns, the White House notes that high-capacity magazines were used in the mass murders at Virginia Tech; Aurora, Colo.; Oak Creek, Wis.; in the fatal Tucson, Ariz., shootings that also gravely wounded then-Rep. Gabrielle Giffords; and at Sandy Hook.

The administration is also proposing to make illegal the possession of armor-piercing bullets, whose manufacture is banned.

4) Target Gun-Trafficking Networks

Obama argues that new laws that target "straw purchasers" of guns by those who traffic in weapons will make prosecutions easier. The White House described this as part of the effort to "get weapons of war off America's streets."

Jonathan Lowy of the Brady Center to Prevent Gun Violence said his organization has never seen the "numbers or intensity of people who are saying enough is enough" as they have since Sandy Hook.

"We need to sensibly address our gun violence problem," Lowy said.

But Congress is a different place than it was in 1994, the last time it passed a gun control measure. Democrats controlled both chambers then; concern about crime was higher on voters' lists of concern; and the assault weapons ban was embedded in a large crime bill that included an expanded death penalty and more funding for police and prisons.

Sandy Hook may have changed things, and changed some minds about guns and the role of government.

In at least two major polls, a bare majority of those surveyed now say that controls on gun ownership are more important than shielding gun rights. An ABC-Washington Post survey conducted in the past week found that 52 percent said the Sandy Hook massacre made them more likely to support some form of gun control, and the same percentage said they somewhat or strongly favor stronger gun laws. This week's Pew survey similarly showed a slim majority favoring gun control.

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