While most of the 12 legislators targeted by the ads are Republicans, some are Democrats from conservative-leaning states, such as rural Western states where hunting and sport shooting are popular.
The Judiciary Committee passed a package of gun laws proposed by Obama in the Newtown attack by a lone gunman.
Proposals in the committee's package included expanding background checks on gun buyers, toughening laws against gun trafficking and straw purchases, banning semi-automatic rifles modeled after military assault weapons as well as large-capacity ammunition magazines, and coming up with ideas for improving school safety.
The weapons ban, which would update a similar 1994 law that expired a decade later, already has been dropped, though Reid, D-Nevada, has promised a floor vote on it as an amendment to the package.
Reid and the White House are pushing hard for expanding background checks to all gun purchases to close a loophole that exempts private sales, such as transactions at gun conventions.
On Tuesday, Reid made a highly personal reference to his own perspective on the issue. Noting that his home state requires a three-day waiting period to pick up a newly purchased gun, Reid contended the delay saved lives.
"Sometimes people in a fit of passion purchase a handgun to do bad things with it -- even as my dad did, kill themselves," he said. "Waiting a few days helps. Requiring a simple background check every time a gun is sold is common sense."
If Republicans managed to filibuster the full gun package, Reid said later that he would find a way to introduce each component individually to force votes.
"It will take a little bit of time but as I've said for months now, the American people deserve a vote -- on background checks, on federal trafficking, on safety in schools, on the size of clips, and yes - assault weapons."
Biden sounded incredulous that Senate Republicans would consider blocking full consideration of legislation that matters to so many Americans, as demonstrated by polls that indicate overwhelming support across the spectrum for expanded background checks.
"A tragedy that traumatized a nation and caught the attention of the entire world ... and the climax of this tragedy could be we're not even going to get a vote?" Biden said, adding "I just don't believe they'll do this."
Keene and other opponents worry that an expanded background check system would create a paper trail that could eventually be used to create a national gun registry, which they reject as unconstitutional.
They also contend it would prove a burden to law-abiding gun owners while doing nothing to stop criminals from getting hold of firearms.
"The one thing you know today is that if the government creates a record, it's not secure," Keene said, adding that requiring background checks on all gun sales -- the so-called universal system -- raised the question of "is it linked to a national registration scheme."
However, Biden accused the NRA of spreading false information that the proposed legislation would intrude on Second Amendment rights.
Some states already have passed stricter gun laws similar to the federal proposals since the Newtown shootings. They include Connecticut, where the killings occurred, and Colorado, the site of two other notorious mass shootings that contributed to a renewed gun debate in America.
The current background check system was created in 1989. It requires federally approved gun dealers to check whether gun buyers have a criminal background or other problem to make them ineligible to purchase a firearm.
Under the system, the gun dealer maintains a record of the transaction, but the federal government keeps no such identifying paperwork.
According to a Justice Department report, less than 2% of those seeking to purchase firearms were denied due to background checks from 1998 through 2009.
Opponents cite that figure as evidence that the system fails to stop illegal weapons sales that the legislation seeks to target, while supporters say the result shows the system keeps some guns out of the hands of the wrong people and the system should be expanded and strengthened.
A Congressional Research Service report last November cited a government report that showed 9,903 of the 14,612 homicides in the nation in 2011 involved firearms.