The assault weapons ban proposed by US President Barack Obama on Wednesday faces quicksand in Congress, where Republicans are in a position to defeat any such a measure.

Instead, lawmakers in the House and Senate could address some of Obama's other proposals, including a universal background check for all gun purchases and a ban on high-capacity magazines.

The debate comes in the aftermath of last month's tragic shooting at Sandy Hook Elementary School in Newtown, Connecticut that left 20 children and six adults dead.

Democratic Senator Dianne Feinstein is preparing to introduce a bill next Thursday that would ban assault weapons like the one used in Newtown.

An earlier time-limited assault weapons ban was pushed through Congress in 1994 and expired 10 years later. Several attempts to reinstate the ban failed.

Republicans control the House, meaning Speaker John Boehner decides what bills get to the floor for a vote.

Unless there is sufficient outside pressure from constituents or an about-face by the party that has been a staunch advocate of gun rights, Obama's proposals could wither on the congressional vine.

"House committees of jurisdiction will review these recommendations. And if the Senate passes a bill, we will also take a look at that," Boehner spokesman Michael Steel said after Obama unveiled his proposals.

Aware of the obstacles, the president urged Americans to pressure their lawmakers into passing tighter gun control legislation.

"If they say no, ask them why not. Ask them what's more important -- doing whatever it takes to get an 'A' grade from the gun lobby that funds their campaigns, or giving parents some peace of mind when they drop their child off for first grade," Obama said.

Several Republican lawmakers expressed frustration with the president's plan, stressing that the Constitution's Second Amendment is non-negotiable.

"Nothing the president is proposing would have stopped the massacre at Sandy Hook," Florida senator Marco Rubio said, adding that it would be wrong to impose "sweeping measures that make it harder for responsible, law-abiding citizens to purchase firearms."

Senator Lindsey Graham said he expected bipartisan opposition to Obama's proposal, and added: "As for reinstating the assault weapons ban, it has already been tried and failed."

Even Senate Majority Leader Harry Reid, a Democrat who has voted in favor of gun rights, acknowledged that a full-on ban would be difficult to achieve.

"Is it something that can pass the Senate? Maybe," Reid told the Nevada Week in Review. "Is it something that can pass the House? I doubt it."

Others questioned the viability of such a ban, given the ubiquity of some of the weapons -- including more than two million AR-15 semi-automatic rifles like the one used in the Sandy Hook massacre.

"This AR-15 that they're all talking about is one of the most popular hunting rifles in the country," Republican congressman Charlie Dent told Politico.

Several Democrats like Joe Manchin of West Virginia are avid hunters and gun rights advocates.

Even if they support "sensible" new gun laws, their vote is complicated by ties to the gun lobby, which supports Democratic moderates, including Reid.

In total, 213 current members of Congress, including 16 Democrats, received checks from the NRA in 2012, according to a study by the Washington Post.

Those who support severe gun restrictions can be assured of a fierce campaign against them.

Some Democrats fear that a gun debate could cost some of their 55 seats in the 100-member Senate. Several in conservative states like West Virginia and Montana face re-election in 2014.

Public opinion, however, is on Obama's side. Two recent polls show a majority of Americans support an assault weapons ban (55 percent in a Pew survey and 58 percent in an ABC/Washington Post survey.

Congressman Keith Ellison was confident a ban could get through Congress -- if Americans speak out.

"We can get it if the people demand it," he told AFP. "Trust me, Harry Reid will change his mind if he gets enough calls demanding greater gun safety."