NEW YORK (AP) — Vice President Joe Biden, Mayor Michael Bloomberg and parents who lost children in the Newtown school massacre met Thursday to redouble efforts for tougher gun restrictions after a setback in Congress, challenging lawmakers to look beyond the politics that appear likely to doom a proposed assault weapons ban.

"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?" Biden asked at a news conference at New York's City Hall. Citing the bloodshed inflicted by a gunman with an assault weapon in Newtown, Conn., he added, "tell me that you can't take off the street these weapons of war."

Biden, who is leading a White House push for new gun laws, and Bloomberg, perhaps the nation's most powerful gun control advocate, met two days after it emerged that the prohibition on military-style firearms would be stripped from a slate of proposals expected to go to the Senate floor next month.

The assault weapons ban has generated the fiercest opposition of any of the measures, and Senate Majority Leader Harry Reid, D-Nev., concluded that it threatened the chances of passing any of them. While Sen. Dianne Feinstein, D-Calif., now plans to propose it as an amendment, Reid has said it's far short of the votes needed to pass.

Still, the roll call will show voters where senators stand, "and then the rest of us have to decide just how we feel about people and their stance," Bloomberg said.

Neil Heslin asked lawmakers to look at the issue from his perspective, as a father whose 6-year-old son, Jesse Lewis, was gunned down at Sandy Hook Elementary School, as were 19 other first-graders and six educators.

"Quite honestly, I'm really ashamed to see that Congress doesn't have the guts to stand up and make a change and put a ban on these type of weapons," he said, his voice low and sometimes halting with emotion. "I never thought something like this could ever happen in Sandy Hook, Connecticut, but it did. And it could happen to any one of your children or grandchildren, in your hometown or your neighborhood."

The Senate Judiciary Committee approved four gun-control measures this month. They include a ban on ammunition magazines carrying more than 10 rounds and on semi-automatic weapons — guns that fire one round and automatically reload — that can take a detachable magazine and have at least one military feature, such as a pistol grip.

The other measures would expand required federal background checks for firearms buyers, increase federal penalties for illegal gun trafficking and boost school safety money.

The National Rifle Association has denounced the assault weapons prohibition as "a senseless ban of firearms based on cosmetic features," and the powerful gun-rights group opposes the background checks provision as opening a door to a national gun registry.

Background checks are now required when licensed gun dealers sell weapons; the proposal would also make them mandatory for transactions between everyday individuals. While some gun-control advocates have coalesced around it as the biggest change likely to pass, Biden reiterated Thursday that the White House is still pressing for the assault weapons ban and the other measures, too.

"I'm not going to rest, and neither is the president, until we do all of these things," he said, maintaining they don't infringe "one iota" on Second Amendment rights. Gun-rights advocates and many Republican lawmakers disagree with him.

The mayor and vice president have conferred on gun control before, but Biden's visit — the first time a vice president has come to City Hall since Walter Mondale in 1979 — was a mark of Bloomberg's stature in the gun control debate. "There has been no support that has been more consequential" than Bloomberg's, the vice president said.

The billionaire mayor has deployed both his public role and his personal fortune to fight for stricter gun laws, co-founding a group of hundreds of mayors to advocate and spending millions of his dollars to support candidates who share his views.