Vice President Biden on Thursday pushed ahead with the White House's pursuit of an assault weapons ban, putting the administration at odds with centrist Democrats who would rather see the legislation die on Capitol Hill.

Even though Senate Majority Leader Harry Reid has already pulled the ban from gun control legislation soon heading to the chamber's floor, Biden was bullish about the prospects for such a prohibition. He reminded the public about the massacre at Sandy Hook Elementary School in Newtown, Conn., saying it would be a disservice to the victims there to give in to political obstacles.

"For all those who say we shouldn't and can't ban assault weapons -- for all those who say the politics is too hard, how can they say that?" asked Biden during a joint news conference with New York City Mayor Michael Bloomberg, a vocal gun control supporter. "When you take a look at those 20 beautiful babies and what happened to them? And those six teachers and administrators?"

Reid on Thursday introduced a gun control bill, which included universal background checks for gun buyers but not the prohibition on high-capacity ammo magazines or a ban on assault weapons that President Obama wants. Reid said senators would be allowed to offer amendments to the bill that add back the missing provisions.

But some analysts questioned why Biden continues to put so much energy into an assault weapons ban when there is dwindling appetite for the measure, even among fellow Democrats.

"Truth be told, this proposal was dead on arrival," said Adam Winkler, a law professor at the University of California, Los Angeles, School of Law and author of the book "Gunfight: The Battle Over the Right to Bear Arms in America." "The Obama administration has wasted a lot of its political capital on the ban on assault weapons. Instead, they should have focused like a laser beam on universal background checks."

Polls show overwhelming public support for universal background checks, and they're considered the most likely option to win bipartisan support.

Reid's decision not to include assault weapons in a broader gun control package enraged many of the activists who hoped to strike a deal before memories of the Newtown massacre fade.

"A lot of my day was spent trying to contain supporters," Ladd Everitt, a spokesman for the Coalition to Stop Gun Violence, said of the reaction to Reid's move. "On one level, it was frustrating, but on another, this isn't bad -- I liked the passion."

Speaking in New York, Biden reminded supporters there was ample opposition to the assault weapons ban proposed before it passed in 1994. That ban expired in 2004.

Bloomberg, who pumped $2 million of his own money into an Illinois special election to defeat a National Rifle Association-endorsed candidate, questioned the backbone of lawmakers resisting gun control efforts.

"The only question," he said, "is whether Congress will have the courage to do the right thing or whether they will allow more innocent people, including innocent children, to be gunned down."